diff --git a/.github/workflows/phpunit.yml b/.github/workflows/phpunit.yml
index 6e8578c..1327a09 100644
--- a/.github/workflows/phpunit.yml
+++ b/.github/workflows/phpunit.yml
@@ -14,6 +14,7 @@ jobs:
       fail-fast: false
       matrix:
         php-version: ['8.1', '8.2', '8.3', '8.4', '8.5']
+        guzzle: ['^7', '^8']
 
     steps:
       - name: Checkout code
@@ -26,7 +27,9 @@ jobs:
           coverage: xdebug
 
       - name: Install dependencies
-        run: composer install --no-interaction --no-progress --prefer-dist
+        run: |
+          composer require "guzzlehttp/guzzle:${{ matrix.guzzle }}" --no-update --no-interaction
+          composer update --no-interaction --no-progress --prefer-dist
 
       - name: Run PHPUnit with coverage
         run: vendor/bin/phpunit --coverage-clover coverage.xml
diff --git a/Tests/Unit/Model/PayOrderTest.php b/Tests/Unit/Model/PayOrderTest.php
index 46735d1..5349430 100644
--- a/Tests/Unit/Model/PayOrderTest.php
+++ b/Tests/Unit/Model/PayOrderTest.php
@@ -2,7 +2,7 @@
 
 declare(strict_types=1);
 
-namespace Tests\Unit;
+namespace Tests\Unit\Model;
 
 use PayNL\Sdk\Model\Amount;
 use PayNL\Sdk\Model\Pay\PayOrder;
diff --git a/Tests/Unit/Model/PayStatusTest.php b/Tests/Unit/Model/PayStatusTest.php
index 634a7c0..1fba6ff 100644
--- a/Tests/Unit/Model/PayStatusTest.php
+++ b/Tests/Unit/Model/PayStatusTest.php
@@ -2,6 +2,8 @@
 
 declare(strict_types=1);
 
+namespace Tests\Unit\Model;
+
 use PayNL\Sdk\Model\Pay\PayStatus;
 use PHPUnit\Framework\TestCase;
 
diff --git a/Tests/Unit/Model/PayloadTest.php b/Tests/Unit/Model/PayloadTest.php
index d158655..00e5eb0 100644
--- a/Tests/Unit/Model/PayloadTest.php
+++ b/Tests/Unit/Model/PayloadTest.php
@@ -2,12 +2,12 @@
 
 declare(strict_types=1);
 
-namespace Tests\Unit;
+namespace Tests\Unit\Model;
 
 use PayNL\Sdk\Model\Pay\PayLoad;
 use PHPUnit\Framework\TestCase;
 
-class PayLoadTest extends TestCase
+class PayloadTest extends TestCase
 {
     public function testLegacyPayloadMapping(): void
     {
diff --git a/Tests/Unit/OrderRequests/OrderApproveRequestTest.php b/Tests/Unit/OrderRequests/OrderApproveRequestTest.php
index 367bd9c..aa21369 100644
--- a/Tests/Unit/OrderRequests/OrderApproveRequestTest.php
+++ b/Tests/Unit/OrderRequests/OrderApproveRequestTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Tests\Unit;
+namespace Tests\Unit\OrderRequests;
 
 use PayNL\Sdk\Model\Pay\PayOrder;
 use PayNL\Sdk\Model\Request\OrderApproveRequest;
diff --git a/Tests/Unit/OrderRequests/OrderCaptureRequestTest.php b/Tests/Unit/OrderRequests/OrderCaptureRequestTest.php
index eed0e68..280277f 100644
--- a/Tests/Unit/OrderRequests/OrderCaptureRequestTest.php
+++ b/Tests/Unit/OrderRequests/OrderCaptureRequestTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Tests\Unit;
+namespace Tests\Unit\OrderRequests;
 
 use PayNL\Sdk\Model\Pay\PayOrder;
 use PayNL\Sdk\Model\Request\OrderCaptureRequest;
diff --git a/Tests/Unit/OrderRequests/OrderCreateRequestTest.php b/Tests/Unit/OrderRequests/OrderCreateRequestTest.php
index 873d4aa..0055f59 100644
--- a/Tests/Unit/OrderRequests/OrderCreateRequestTest.php
+++ b/Tests/Unit/OrderRequests/OrderCreateRequestTest.php
@@ -2,7 +2,7 @@
 
 declare(strict_types=1);
 
-namespace Tests\Unit;
+namespace Tests\Unit\OrderRequests;
 
 use PayNL\Sdk\Model\Amount;
 use PayNL\Sdk\Model\Customer;
@@ -23,7 +23,6 @@ public function testEnableFastCheckout(): void
 
         $reflection = new \ReflectionClass($request);
         $optimizeProperty = $reflection->getProperty('optimize');
-        $optimizeProperty->setAccessible(true);
 
         $this->assertEquals([
             'flow' => 'fastCheckout',
@@ -43,7 +42,6 @@ public function testSetReturnUrl(): void
 
         $reflection = new \ReflectionClass($request);
         $returnUrlProperty = $reflection->getProperty('returnUrl');
-        $returnUrlProperty->setAccessible(true);
 
         $this->assertEquals('https://example.com/return', $returnUrlProperty->getValue($request));
     }
@@ -58,7 +56,6 @@ public function testSetAmount(): void
 
         $reflection = new \ReflectionClass($request);
         $amountProperty = $reflection->getProperty('amount');
-        $amountProperty->setAccessible(true);
 
         $this->assertEquals(12345, $amountProperty->getValue($request));
     }
@@ -73,10 +70,8 @@ public function testSetAmountUsingObject(): void
 
         $reflection = new \ReflectionClass($request);
         $amountProperty = $reflection->getProperty('amount');
-        $amountProperty->setAccessible(true);
 
         $currencyProperty = $reflection->getProperty('currency');
-        $currencyProperty->setAccessible(true);
 
         $this->assertEquals(12345, $amountProperty->getValue($request));
         $this->assertEquals('EUR', $currencyProperty->getValue($request));
@@ -94,7 +89,6 @@ public function testSetReference(): void
 
         $reflection = new \ReflectionClass($request);
         $referenceProperty = $reflection->getProperty('reference');
-        $referenceProperty->setAccessible(true);
 
         $this->assertEquals('Order123', $referenceProperty->getValue($request));
     }
@@ -124,9 +118,7 @@ public function testSetNotification(): void
 
         $reflection = new \ReflectionClass($request);
         $notificationTypeProperty = $reflection->getProperty('notificationType');
-        $notificationTypeProperty->setAccessible(true);
         $notificationRecipientProperty = $reflection->getProperty('notificationRecipient');
-        $notificationRecipientProperty->setAccessible(true);
 
         $this->assertEquals('email', $notificationTypeProperty->getValue($request));
         $this->assertEquals('test@example.com', $notificationRecipientProperty->getValue($request));
@@ -170,7 +162,6 @@ public function testSetCustomer(): void
 
         $reflection = new \ReflectionClass($request);
         $customerProperty = $reflection->getProperty('customer');
-        $customerProperty->setAccessible(true);
 
         $this->assertSame($mockCustomer, $customerProperty->getValue($request));
     }
@@ -187,7 +178,6 @@ public function testSetOrder(): void
 
         $reflection = new \ReflectionClass($request);
         $orderProperty = $reflection->getProperty('order');
-        $orderProperty->setAccessible(true);
 
         $this->assertSame($mockOrder, $orderProperty->getValue($request));
     }
@@ -204,7 +194,6 @@ public function testSetStats(): void
 
         $reflection = new \ReflectionClass($request);
         $statsProperty = $reflection->getProperty('stats');
-        $statsProperty->setAccessible(true);
 
         $this->assertSame($mockStats, $statsProperty->getValue($request));
     }
diff --git a/Tests/Unit/OrderRequests/OrderStatusRequestTest.php b/Tests/Unit/OrderRequests/OrderStatusRequestTest.php
index a46acaf..7536c9c 100644
--- a/Tests/Unit/OrderRequests/OrderStatusRequestTest.php
+++ b/Tests/Unit/OrderRequests/OrderStatusRequestTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Tests\Unit;
+namespace Tests\Unit\OrderRequests;
 
 use PayNL\Sdk\Model\Pay\PayOrder;
 use PayNL\Sdk\Model\Request\OrderStatusRequest;
diff --git a/Tests/Unit/OrderRequests/OrderVoidRequestTest.php b/Tests/Unit/OrderRequests/OrderVoidRequestTest.php
index 86326e1..c1ecc37 100644
--- a/Tests/Unit/OrderRequests/OrderVoidRequestTest.php
+++ b/Tests/Unit/OrderRequests/OrderVoidRequestTest.php
@@ -2,6 +2,8 @@
 
 declare(strict_types=1);
 
+namespace Tests\Unit\OrderRequests;
+
 use PayNL\Sdk\Model\Pay\PayOrder;
 use PayNL\Sdk\Model\Request\OrderVoidRequest;
 use PayNL\Sdk\Request\RequestData;
diff --git a/Tests/Unit/OrderRequests/ServiceGetConfigRequestTest.php b/Tests/Unit/OrderRequests/ServiceGetConfigRequestTest.php
index bb9ebca..78b3ca8 100644
--- a/Tests/Unit/OrderRequests/ServiceGetConfigRequestTest.php
+++ b/Tests/Unit/OrderRequests/ServiceGetConfigRequestTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Tests\Unit;
+namespace Tests\Unit\OrderRequests;
 
 use PayNL\Sdk\Model\Request\ServiceGetConfigRequest;
 use PayNL\Sdk\Model\Response\ServiceGetConfigResponse;
diff --git a/Tests/Unit/OrderRequests/ServiceGetConfigResponseTest.php b/Tests/Unit/OrderRequests/ServiceGetConfigResponseTest.php
index f6e0a24..275708a 100644
--- a/Tests/Unit/OrderRequests/ServiceGetConfigResponseTest.php
+++ b/Tests/Unit/OrderRequests/ServiceGetConfigResponseTest.php
@@ -2,6 +2,8 @@
 
 declare(strict_types=1);
 
+namespace Tests\Unit\OrderRequests;
+
 use PayNL\Sdk\Model\CheckoutOptions;
 use PayNL\Sdk\Model\Method;
 use PayNL\Sdk\Model\Response\ServiceGetConfigResponse;
diff --git a/Tests/Unit/OrderRequests/TerminalsBrowseRequestTest.php b/Tests/Unit/OrderRequests/TerminalsBrowseRequestTest.php
index 2c6388d..d2ef82d 100644
--- a/Tests/Unit/OrderRequests/TerminalsBrowseRequestTest.php
+++ b/Tests/Unit/OrderRequests/TerminalsBrowseRequestTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Tests\Unit;
+namespace Tests\Unit\OrderRequests;
 
 use PayNL\Sdk\Application\Application;
 use PayNL\Sdk\Config\Config;
diff --git a/Tests/Unit/OrderRequests/TerminalsGetRequestTest.php b/Tests/Unit/OrderRequests/TerminalsGetRequestTest.php
index cb511b5..13bc744 100644
--- a/Tests/Unit/OrderRequests/TerminalsGetRequestTest.php
+++ b/Tests/Unit/OrderRequests/TerminalsGetRequestTest.php
@@ -2,7 +2,7 @@
 
 declare(strict_types=1);
 
-namespace Tests\Unit;
+namespace Tests\Unit\OrderRequests;
 
 use PayNL\Sdk\Model\Request\TerminalsGetRequest;
 use PHPUnit\Framework\TestCase;
diff --git a/Tests/Unit/OrderRequests/TransactionRefundResponseTest.php b/Tests/Unit/OrderRequests/TransactionRefundResponseTest.php
index 3d67630..742b6c3 100644
--- a/Tests/Unit/OrderRequests/TransactionRefundResponseTest.php
+++ b/Tests/Unit/OrderRequests/TransactionRefundResponseTest.php
@@ -2,6 +2,8 @@
 
 declare(strict_types=1);
 
+namespace Tests\Unit\OrderRequests;
+
 use PayNL\Sdk\Model\Amount;
 use PayNL\Sdk\Model\Response\TransactionRefundResponse;
 use PHPUnit\Framework\TestCase;
diff --git a/Tests/Unit/OrderRequests/TransactionStatusResponseTest.php b/Tests/Unit/OrderRequests/TransactionStatusResponseTest.php
index a9dc311..7a38386 100644
--- a/Tests/Unit/OrderRequests/TransactionStatusResponseTest.php
+++ b/Tests/Unit/OrderRequests/TransactionStatusResponseTest.php
@@ -2,6 +2,8 @@
 
 declare(strict_types=1);
 
+namespace Tests\Unit\OrderRequests;
+
 use PayNL\Sdk\Model\Amount;
 use PayNL\Sdk\Model\Response\TransactionStatusResponse;
 use PHPUnit\Framework\TestCase;
diff --git a/Tests/Unit/OrderRequests/VoucherInfoRequestTest.php b/Tests/Unit/OrderRequests/VoucherInfoRequestTest.php
index 1f78925..da11efc 100644
--- a/Tests/Unit/OrderRequests/VoucherInfoRequestTest.php
+++ b/Tests/Unit/OrderRequests/VoucherInfoRequestTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Tests\Unit;
+namespace Tests\Unit\OrderRequests;
 
 use PayNL\Sdk\Application\Application;
 use PayNL\Sdk\Config\Config;
@@ -61,7 +61,6 @@ public function testSetServiceId(): void
         $request->setServiceId('SL-1234-5678');
         $reflection = new \ReflectionClass($request);
         $serviceIdProperty = $reflection->getProperty('serviceId');
-        $serviceIdProperty->setAccessible(true);
 
         $this->assertEquals('SL-1234-5678', $serviceIdProperty->getValue($request));
     }
@@ -77,7 +76,6 @@ public function testSetCardNumber(): void
         $request->setCardNumber('1234-5678-9012-3456');
         $reflection = new \ReflectionClass($request);
         $cardNumberProperty = $reflection->getProperty('cardNumber');
-        $cardNumberProperty->setAccessible(true);
 
         $this->assertEquals('1234-5678-9012-3456', $cardNumberProperty->getValue($request));
     }
@@ -93,7 +91,6 @@ public function testSetPinCode(): void
         $request->setPinCode('123456');
         $reflection = new \ReflectionClass($request);
         $pinCodeProperty = $reflection->getProperty('pinCode');
-        $pinCodeProperty->setAccessible(true);
 
         $this->assertEquals('123456', $pinCodeProperty->getValue($request));
     }
@@ -109,7 +106,6 @@ public function testSetPointOfInteraction(): void
         $request->setPointOfInteraction('ON_THE_MOVE');
         $reflection = new \ReflectionClass($request);
         $poiProperty = $reflection->getProperty('pointOfInteraction');
-        $poiProperty->setAccessible(true);
 
         $this->assertEquals('ON_THE_MOVE', $poiProperty->getValue($request));
     }
diff --git a/Tests/Unit/OrderRequests/VoucherPaymentRequestTest.php b/Tests/Unit/OrderRequests/VoucherPaymentRequestTest.php
index 8ccdcab..b828c45 100644
--- a/Tests/Unit/OrderRequests/VoucherPaymentRequestTest.php
+++ b/Tests/Unit/OrderRequests/VoucherPaymentRequestTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Tests\Unit;
+namespace Tests\Unit\OrderRequests;
 
 use PayNL\Sdk\Application\Application;
 use PayNL\Sdk\Config\Config;
@@ -62,7 +62,6 @@ public function testSetCardNumber(): void
         $request->setCardNumber('1234-5678-9012-3456');
         $reflection = new \ReflectionClass($request);
         $cardNumberProperty = $reflection->getProperty('cardNumber');
-        $cardNumberProperty->setAccessible(true);
 
         $this->assertEquals('1234-5678-9012-3456', $cardNumberProperty->getValue($request));
     }
@@ -78,7 +77,6 @@ public function testSetPinCode(): void
         $request->setPinCode('123456');
         $reflection = new \ReflectionClass($request);
         $pinCodeProperty = $reflection->getProperty('pinCode');
-        $pinCodeProperty->setAccessible(true);
 
         $this->assertEquals('123456', $pinCodeProperty->getValue($request));
     }
@@ -94,7 +92,6 @@ public function testSetPointOfInteraction(): void
         $request->setPointOfInteraction('ON_THE_MOVE');
         $reflection = new \ReflectionClass($request);
         $poiProperty = $reflection->getProperty('pointOfInteraction');
-        $poiProperty->setAccessible(true);
 
         $this->assertEquals('ON_THE_MOVE', $poiProperty->getValue($request));
     }
diff --git a/Tests/Unit/Request/AbstractRequestExecuteTest.php b/Tests/Unit/Request/AbstractRequestExecuteTest.php
new file mode 100644
index 0000000..fa31974
--- /dev/null
+++ b/Tests/Unit/Request/AbstractRequestExecuteTest.php
@@ -0,0 +1,65 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Unit\Request;
+
+use GuzzleHttp\Client;
+use GuzzleHttp\Handler\MockHandler;
+use GuzzleHttp\HandlerStack;
+use GuzzleHttp\Psr7\Response as GuzzleResponse;
+use PayNL\Sdk\Request\Request;
+use PayNL\Sdk\Response\Response;
+use PHPUnit\Framework\TestCase;
+
+class AbstractRequestExecuteTest extends TestCase
+{
+    public function testExecuteSendsGetAgainstClientBaseUri(): void
+    {
+        $mock = new MockHandler([
+            new GuzzleResponse(200, ['Content-Type' => 'application/json'], '{"id":"1"}'),
+        ]);
+        $client = new Client([
+            'handler' => HandlerStack::create($mock),
+            'base_uri' => 'https://rest.pay.nl/v2/',
+        ]);
+
+        $request = new Request('orders', Request::METHOD_GET);
+        $request->applyClient($client, 'https://rest.pay.nl/v2/');
+
+        $response = new Response();
+        $request->execute($response);
+
+        $this->assertSame(200, $response->getStatusCode());
+        $this->assertSame('{"id":"1"}', $response->getRawBody());
+
+        $lastRequest = $mock->getLastRequest();
+        $this->assertNotNull($lastRequest);
+        $this->assertSame('GET', $lastRequest->getMethod());
+        $this->assertSame('https://rest.pay.nl/v2/orders', (string)$lastRequest->getUri());
+    }
+
+    public function testExecuteUsesAbsoluteUriWhenUrlOptionIsSet(): void
+    {
+        $mock = new MockHandler([
+            new GuzzleResponse(200, ['Content-Type' => 'application/json'], '{"ok":true}'),
+        ]);
+        $client = new Client([
+            'handler' => HandlerStack::create($mock),
+            'base_uri' => 'https://rest.pay.nl/v2/',
+        ]);
+
+        $request = new Request('orders', Request::METHOD_POST, [], ['url' => 'https://failover.pay.nl']);
+        $request->applyClient($client, 'https://rest.pay.nl/v2/');
+
+        $response = new Response();
+        $request->execute($response);
+
+        $this->assertSame(200, $response->getStatusCode());
+
+        $lastRequest = $mock->getLastRequest();
+        $this->assertNotNull($lastRequest);
+        $this->assertSame('POST', $lastRequest->getMethod());
+        $this->assertSame('https://failover.pay.nl/orders', (string)$lastRequest->getUri());
+    }
+}
diff --git a/Tests/Unit/Response/VoucherInfoResponseTest.php b/Tests/Unit/Response/VoucherInfoResponseTest.php
index 9b2d4b8..3038153 100644
--- a/Tests/Unit/Response/VoucherInfoResponseTest.php
+++ b/Tests/Unit/Response/VoucherInfoResponseTest.php
@@ -2,7 +2,7 @@
 
 declare(strict_types=1);
 
-namespace Tests\Unit;
+namespace Tests\Unit\Response;
 
 use PayNL\Sdk\Model\Amount;
 use PayNL\Sdk\Model\Response\VoucherInfoResponse;
diff --git a/Tests/Unit/Util/ExchangeResponseTest.php b/Tests/Unit/Util/ExchangeResponseTest.php
index a71126f..ef6537a 100644
--- a/Tests/Unit/Util/ExchangeResponseTest.php
+++ b/Tests/Unit/Util/ExchangeResponseTest.php
@@ -2,6 +2,8 @@
 
 declare(strict_types=1);
 
+namespace Tests\Unit\Util;
+
 use PayNL\Sdk\Util\ExchangeResponse;
 use PHPUnit\Framework\TestCase;
 
@@ -11,7 +13,6 @@ private function getProperty(object $object, string $name): mixed
     {
         $ref = new \ReflectionClass($object);
         $prop = $ref->getProperty($name);
-        $prop->setAccessible(true);
 
         return $prop->getValue($object);
     }
diff --git a/Tests/Unit/Util/ExchangeTest.php b/Tests/Unit/Util/ExchangeTest.php
index e8b7b8a..534548d 100644
--- a/Tests/Unit/Util/ExchangeTest.php
+++ b/Tests/Unit/Util/ExchangeTest.php
@@ -2,7 +2,7 @@
 
 declare(strict_types=1);
 
-namespace Tests\Unit;
+namespace Tests\Unit\Util;
 
 use PayNL\Sdk\Util\Exchange;
 use PayNL\Sdk\Util\ExchangeResponse;
@@ -25,7 +25,6 @@ private function setHeaders(Exchange $exchange, array $headers): void
     {
         $refClass = new ReflectionClass(Exchange::class);
         $prop     = $refClass->getProperty('headers');
-        $prop->setAccessible(true);
         $prop->setValue($exchange, $headers);
     }
 
@@ -107,6 +106,22 @@ public function testIsSignExchangeFalseWhenSignatureMethodMissingOrNotHmac(): vo
         $this->assertFalse($exchange->isSignExchange());
     }
 
+    public function testIsSignExchangeReadsSignatureMethodFromServer(): void
+    {
+        $previous = $_SERVER['HTTP_SIGNATURE_METHOD'] ?? null;
+        $_SERVER['HTTP_SIGNATURE_METHOD'] = 'HMAC';
+
+        try {
+            $this->assertTrue($this->createExchange()->isSignExchange());
+        } finally {
+            if ($previous === null) {
+                unset($_SERVER['HTTP_SIGNATURE_METHOD']);
+            } else {
+                $_SERVER['HTTP_SIGNATURE_METHOD'] = $previous;
+            }
+        }
+    }
+
     public function testCheckSignExchangeReturnsFalseWhenNotSigningExchange(): void
     {
         $exchange = $this->createExchange();
diff --git a/Tests/Unit/Util/PayCacheTest.php b/Tests/Unit/Util/PayCacheTest.php
index 70188a2..8bf6937 100644
--- a/Tests/Unit/Util/PayCacheTest.php
+++ b/Tests/Unit/Util/PayCacheTest.php
@@ -2,6 +2,8 @@
 
 declare(strict_types=1);
 
+namespace Tests\Unit\Util;
+
 use PayNL\Sdk\Util\PayCache;
 use PHPUnit\Framework\TestCase;
 
@@ -11,7 +13,6 @@ private function invokeMethod(object $object, string $method, array $args = []):
     {
         $refClass = new \ReflectionClass($object);
         $refMethod = $refClass->getMethod($method);
-        $refMethod->setAccessible(true);
 
         return $refMethod->invokeArgs($object, $args);
     }
diff --git a/Tests/Unit/Util/VatFunctionsTest.php b/Tests/Unit/Util/VatFunctionsTest.php
index a8abbc0..60c60e4 100644
--- a/Tests/Unit/Util/VatFunctionsTest.php
+++ b/Tests/Unit/Util/VatFunctionsTest.php
@@ -2,7 +2,7 @@
 
 declare(strict_types=1);
 
-namespace Tests\Unit;
+namespace Tests\Unit\Util;
 
 use PHPUnit\Framework\TestCase;
 
diff --git a/composer.json b/composer.json
index de8ee31..764a3bc 100644
--- a/composer.json
+++ b/composer.json
@@ -7,7 +7,7 @@
     "php": "^8.1",
     "ext-curl": "*",
     "ext-json": "*",
-    "guzzlehttp/guzzle": "^7",
+    "guzzlehttp/guzzle": "^7 || ^8",
     "psr/container": "^2 || ^1",
     "psr/http-message": "^2 || ^1"
   },
@@ -46,7 +46,7 @@
   },
   "autoload-dev": {
     "psr-4": {
-      "Tests\\": "tests/"
+      "Tests\\": "Tests/"
     }
   },
   "minimum-stability": "dev",
@@ -62,8 +62,10 @@
   },
   "scripts": {
     "test": [
+      "@phpunit",
       "@style-check"
     ],
+    "phpunit": "vendor/bin/phpunit",
     "style-check": [
       "@phpstan",
       "@phpcs"
diff --git a/phpcs.xml b/phpcs.xml
index 2c11b4e..b6106db 100644
--- a/phpcs.xml
+++ b/phpcs.xml
@@ -17,7 +17,7 @@
         <exclude name="Squiz.Commenting.FunctionComment.MissingParamComment" />
         <exclude name="Squiz.Commenting.FunctionComment.MissingParamTag" />
         <exclude name="Squiz.Commenting.FunctionComment.MissingReturn" />
-        <exclude name="Squiz.Commenting.FunctionComment.TypeHintMissing" />-->
+        <exclude name="Squiz.Commenting.FunctionComment.TypeHintMissing" />
     </rule>
 
     <rule ref="SlevomatCodingStandard.TypeHints.DeclareStrictTypes">
diff --git a/src/Api/Api.php b/src/Api/Api.php
index e36e56c..d03f6bc 100644
--- a/src/Api/Api.php
+++ b/src/Api/Api.php
@@ -101,7 +101,11 @@ protected function setAuthAdapter(AuthAdapterInterface $adapter): self
     public function doHandle(RequestInterface $request, Response $response): Response
     {
         $format = $request->getFormat();
-        $request->applyClient($this->getClient());
+        if ($request instanceof AbstractRequest) {
+            $request->applyClient($this->getClient(), $this->getConfiguredBaseUri());
+        } else {
+            $request->applyClient($this->getClient());
+        }
 
         # Apply the correct headers based on the formats set on request and response object
         # and also add the authentication header which is based on the authentication adapter
@@ -126,4 +130,21 @@ public function doHandle(RequestInterface $request, Response $response): Respons
 
         return $response;
     }
+
+    /**
+     * @return string
+     */
+    private function getConfiguredBaseUri(): string
+    {
+        $api = $this->getOption('api');
+        if (!is_array($api)) {
+            return '';
+        }
+
+        $url = rtrim((string)($api['url'] ?? ''), '/');
+        $version = $api['version'] ?? '';
+        $pathVersion = $version === '' ? '' : '/v' . $version;
+
+        return $url . $pathVersion . '/';
+    }
 }
diff --git a/src/Request/AbstractRequest.php b/src/Request/AbstractRequest.php
index c28cb6c..993d67a 100644
--- a/src/Request/AbstractRequest.php
+++ b/src/Request/AbstractRequest.php
@@ -27,7 +27,7 @@
 };
 use GuzzleHttp\Client;
 use GuzzleHttp\Exception\GuzzleException;
-use GuzzleHttp\Exception\RequestException;
+use GuzzleHttp\Psr7\Request as Psr7Request;
 
 /**
  * Class AbstractRequest
@@ -82,6 +82,11 @@ abstract class AbstractRequest implements
      */
     protected $client;
 
+    /**
+     * @var string
+     */
+    protected $clientBaseUri = '';
+
     /**
      * @var array
      */
@@ -333,11 +338,13 @@ public function setBody(mixed $body): self
 
     /**
      * @param Client $client
+     * @param string $baseUri
      * @return $this
      */
-    public function applyClient(Client $client): self
+    public function applyClient(Client $client, string $baseUri = ''): self
     {
         $this->client = $client;
+        $this->clientBaseUri = $baseUri;
         return $this;
     }
 
@@ -435,28 +442,35 @@ public function execute(Response $response): void
         $filters = $this->getFilters();
 
         $uri = trim($uri . '?' . implode('&', $filters), '?');
-        $url = $this->getOption('url');
+        $overrideUrl = $this->getOption('url');
+        $baseUri = is_string($overrideUrl) && $overrideUrl !== ''
+            ? $overrideUrl
+            : (string)$this->clientBaseUri;
 
         $this->dumpPreStringAdvanced($this->getBody(), 'Request body', 400);
 
+        $requestBody = '';
+        $curlRequest = '';
+        $rawBody = '';
+        $body = '';
+        $statusCode = 500;
+
         try {
             $guzzleClient = $this->getClient();
             if (false === ($guzzleClient instanceof Client)) {
                 throw new RuntimeException('No HTTP client found', 500);
             }
 
-            if (!empty($url)) {
-                $guzzleConfig = $guzzleClient->getConfig();
-                # This also will override the version
-                $guzzleConfig['base_uri'] = $url;
-                $guzzleClient = new Client($guzzleConfig);
-            }
             $requestBody = $this->getBody();
+            $method = strtoupper($this->getMethod());
+            $requestUri = $uri;
+            if (is_string($overrideUrl) && $overrideUrl !== '') {
+                $requestUri = rtrim($overrideUrl, '/') . '/' . $uri;
+            }
 
-            # Create a Guzzle PSR 7 Request
-            $guzzleRequest = new \GuzzleHttp\Psr7\Request($this->getMethod(), $uri, $this->getHeaders(), $requestBody);
+            $guzzleRequest = new Psr7Request($method, $requestUri, $this->getHeaders(), $requestBody);
 
-            $curlRequest = 'curl -X ' . $this->getMethod() . ' ' . $guzzleClient->getConfig('base_uri') . $uri;
+            $curlRequest = 'curl -X ' . $method . ' ' . rtrim((string)$baseUri, '/') . '/' . $uri;
             foreach ($this->getHeaders() as $headerfield => $headervalue) {
                 $curlRequest .= ' -H "' . $headerfield . ': ' . $headervalue . '"';
             }
@@ -464,39 +478,18 @@ public function execute(Response $response): void
             $curlRequest .= empty($requestBody) ? '' : ' -d \'' . $requestBody . '\'';
 
             $this->dumpPreString($curlRequest, 'Curl request');
-            $this->dumpPreString(rtrim((string)$guzzleClient->getConfig('base_uri'), '/') . '/' . $guzzleRequest->getUri(), 'Requested URL');
+            $this->dumpPreString(rtrim((string)$baseUri, '/') . '/' . $guzzleRequest->getUri(), 'Requested URL');
             $this->dumpPreString(implode(PHP_EOL, array_map(static function ($item, $key) {
                 return "{$key}: {$item}";
             }, $this->getHeaders(), array_keys($this->getHeaders()))), 'Headers');
 
-            $guzzleResponse = $guzzleClient->send($guzzleRequest);
-
+            $guzzleResponse = $guzzleClient->send($guzzleRequest, ['http_errors' => false]);
             $rawBody = $guzzleResponse->getBody()->getContents();
-
             $statusCode = $guzzleResponse->getStatusCode();
             $body = $rawBody;
-        } catch (RequestException $re) {
-            $errorMessages = '';
-            $rawBody = $re->getMessage();
-
-            if (null !== $re->getResponse()) {
-                $guzzleExceptionBody = $re->getResponse()->getBody();
-                $size = $guzzleExceptionBody->isSeekable() === true ? (int)$guzzleExceptionBody->getSize() : 0;
-
-                if (0 < $size) {
-                    $content = $guzzleExceptionBody->read($size);
-                    $guzzleExceptionBody->rewind();
-
-                    $errorMessages = $content;
-                }
-
-                $rawBody = $errorMessages;
-            }
 
-            $statusCode = $re->getCode();
-            $body = '';
-            if ('' !== $errorMessages) {
-                $body = $this->getErrorsString($response->getFormat(), (int)$statusCode, $errorMessages);
+            if ($statusCode >= 400 && $rawBody !== '') {
+                $body = $this->getErrorsString($response->getFormat(), $statusCode, $rawBody);
             }
         } catch (GuzzleException | ExceptionInterface $e) {
             $statusCode = $e->getCode() ?: 500;
@@ -505,7 +498,7 @@ public function execute(Response $response): void
         }
 
         if (function_exists('displayPayRequest')) {
-            displayPayRequest($guzzleClient->getConfig('base_uri') . $uri, $requestBody ?? '', $rawBody, $curlRequest ?? '');
+            displayPayRequest(rtrim((string)$baseUri, '/') . '/' . $uri, $requestBody, $rawBody, $curlRequest);
         }
 
         $response->setStatusCode($statusCode)->setRawBody($rawBody)->setBody($body);
diff --git a/src/Util/Exchange.php b/src/Util/Exchange.php
index b74073a..f66924e 100644
--- a/src/Util/Exchange.php
+++ b/src/Util/Exchange.php
@@ -451,7 +451,24 @@ public function isSignExchange(): bool
     private function getRequestHeaders(): bool|array|string
     {
         if (empty($this->headers)) {
-            $this->headers = array_change_key_case(getallheaders());
+            $headers = [];
+            foreach ($_SERVER as $name => $value) {
+                if (!is_string($name)) {
+                    continue;
+                }
+                if (str_starts_with($name, 'HTTP_')) {
+                    $headers[str_replace('_', '-', substr($name, 5))] = $value;
+                    continue;
+                }
+                if ($name === 'CONTENT_TYPE') {
+                    $headers['Content-Type'] = $value;
+                    continue;
+                }
+                if ($name === 'CONTENT_LENGTH') {
+                    $headers['Content-Length'] = $value;
+                }
+            }
+            $this->headers = array_change_key_case($headers);
         }
         return $this->headers;
     }