diff --git a/src/features/chat/api/room.ts b/src/features/chat/api/room.ts
index 21dbfd4..ef1cf3e 100644
--- a/src/features/chat/api/room.ts
+++ b/src/features/chat/api/room.ts
@@ -4,12 +4,12 @@ import type { ChatProduct, ChatRole, SaleStatus, TradeStatus } from '../model/ty
 import type { ChatRoomDetailResponse, ProductStatus } from './dto';
 
 // 채팅방 생성 또는 조회 (아이템 상세 페이지 채팅하기 버튼).
-// 판매자가 받은 구매 제안 상세에서 열 땐 purchaseOfferId를 함께 보내 제안자↔소유자 방을 잡는다.
 export const createOrGetChatRoom = (itemId: number, purchaseOfferId?: number) =>
-  api.post<{ chatRoomId: number }>('/chats', {
-    itemId,
-    ...(purchaseOfferId != null && { purchaseOfferId }),
-  });
+  api.post<{ chatRoomId: number }>('/chats', { itemId, purchaseOfferId });
+
+// 채팅방 생성 또는 조회 (거래 상세 페이지 채팅하기 버튼).
+export const createOrGetChatRoomByTrade = (tradeId: number) =>
+  api.post<{ chatRoomId: number }>(`/chats/trades/${tradeId}`);
 
 // 채팅방 상세 조회 (프로덕트 바 데이터)
 export const getChatRoom = (chatRoomId: number) => {
diff --git a/src/features/ootd/ui/OotdTagEditor.tsx b/src/features/ootd/ui/OotdTagEditor.tsx
index 94832a2..7958655 100644
--- a/src/features/ootd/ui/OotdTagEditor.tsx
+++ b/src/features/ootd/ui/OotdTagEditor.tsx
@@ -8,6 +8,8 @@ import { getItemDetail } from '@/features/mypage/api/itemsApi';
 import type { ItemDetailResponse } from '@/features/mypage/model/items';
 import { getDaysAgo } from '@/features/mypage/lib/daysAgo';
 import { resolveFileUrl } from '@/shared/lib/resolveFileUrl';
+import { Toast } from '@/shared/components';
+import { useToast } from '@/shared/hooks/useToast';
 import TagLoading from '@/pages/camera/component/TagLoading';
 import TagResultSheet, {
   MIDDLE as RESULT_SHEET_DEFAULT_H,
@@ -43,6 +45,7 @@ type Props = {
   className?: string;
 };
 
+const MAX_TAGS = 5; // 한 게시물에 붙일 수 있는 최대 태그 수
 const BOX_W = 0.26;
 const BOX_H = 0.22;
 const clamp = (v: number, min: number, max: number) => Math.min(Math.max(v, min), max);
@@ -140,6 +143,7 @@ const OotdTagEditor = ({
   const [query, setQuery] = useState('');
   const [newItemOpen, setNewItemOpen] = useState(false);
   const [showBox, setShowBox] = useState(true);
+  const { message: toastMessage, show: showToast, hide: hideToast } = useToast();
 
   const activeBox = boxes.find((b) => b.id === activeBoxId) ?? null;
   const tagCount = boxes.filter((b) => b.itemId).length; // 아이템 부착된 박스 = 완성 태그
@@ -266,6 +270,11 @@ const OotdTagEditor = ({
   // 이미지 빈 곳 탭 → 그 위치에 박스 생성 + 활성화 + 분석 API 호출
   const handleAreaClick = (e: MouseEvent<HTMLDivElement>) => {
     if ((e.target as HTMLElement).dataset.tagArea !== 'true') return; // 박스/버튼 클릭은 무시
+    // 완성 태그가 최대치면 새 박스 생성 차단 (기존 태그 편집/이동은 그대로)
+    if (tagCount >= MAX_TAGS) {
+      showToast(`태그는 최대 ${MAX_TAGS}개까지 추가할 수 있어요.`);
+      return;
+    }
     const rect = e.currentTarget.getBoundingClientRect();
     const cx = (e.clientX - rect.left) / rect.width;
     const cy = (e.clientY - rect.top) / rect.height;
@@ -401,6 +410,8 @@ const OotdTagEditor = ({
           onSubmit={handleRegister}
         />
       )}
+
+      <Toast message={toastMessage} onClose={hideToast} />
     </div>
   );
 };
diff --git a/src/pages/mypage/AddressFormPage.tsx b/src/pages/mypage/AddressFormPage.tsx
index 58473d9..ba261b6 100644
--- a/src/pages/mypage/AddressFormPage.tsx
+++ b/src/pages/mypage/AddressFormPage.tsx
@@ -36,7 +36,7 @@ const AddressFormPage = () => {
 
   if (isEditMode && isPending) {
     return (
-      <div className="mx-auto min-h-screen w-full max-w-[390px] bg-[#FFFFFF] font-sans">
+      <div className="mx-auto min-h-dvh w-full max-w-[390px] bg-[#FFFFFF] font-sans">
         <FormHeader title="배송지 수정" onBack={() => navigate(-1)} />
         <p className="px-[16px] py-[24px] text-center text-[13px] text-[#767676]">불러오는 중...</p>
       </div>
@@ -47,7 +47,7 @@ const AddressFormPage = () => {
 
   if (isEditMode && !target) {
     return (
-      <div className="mx-auto min-h-screen w-full max-w-[390px] bg-[#FFFFFF] font-sans">
+      <div className="mx-auto min-h-dvh w-full max-w-[390px] bg-[#FFFFFF] font-sans">
         <FormHeader title="배송지 수정" onBack={() => navigate(-1)} />
         <p className="px-[16px] py-[24px] text-center text-[13px] text-[#767676]">
           배송지 정보를 찾을 수 없습니다.
@@ -123,7 +123,7 @@ const AddressForm = ({ addressId, initial, onDone }: AddressFormProps) => {
   };
 
   return (
-    <div className="mx-auto min-h-screen w-full max-w-[390px] bg-[#FFFFFF] font-sans">
+    <div className="mx-auto min-h-dvh w-full max-w-[390px] bg-[#FFFFFF] font-sans">
       <FormHeader title={isEditMode ? '배송지 수정' : '배송지 추가'} onBack={onDone} />
 
       <div className="flex flex-col gap-[16px] px-[16px] py-[24px]">
diff --git a/src/pages/mypage/AddressManagePage.tsx b/src/pages/mypage/AddressManagePage.tsx
index f7b44d7..2872c2e 100644
--- a/src/pages/mypage/AddressManagePage.tsx
+++ b/src/pages/mypage/AddressManagePage.tsx
@@ -23,7 +23,7 @@ const AddressManagePage = () => {
   };
 
   return (
-    <div className="relative mx-auto min-h-screen w-full max-w-[390px] bg-[#FFFFFF] font-sans">
+    <div className="relative mx-auto min-h-dvh w-full max-w-[390px] bg-[#FFFFFF] font-sans">
       <header className="flex h-[52px] items-center border-b border-[#F0F0F0] px-[16px]">
         <button type="button" onClick={() => navigate(-1)} aria-label="뒤로가기">
           <ChevronLeft size={24} className="text-[#111111]" />
diff --git a/src/pages/mypage/TradeDetailPage.tsx b/src/pages/mypage/TradeDetailPage.tsx
index ba83116..44a761d 100644
--- a/src/pages/mypage/TradeDetailPage.tsx
+++ b/src/pages/mypage/TradeDetailPage.tsx
@@ -8,7 +8,7 @@ import { useTradeStatusChange } from '@/features/trade/api/useTradeStatusChange'
 import type { TradeStatus } from '@/features/trade/api/types';
 import { buildTradeTimeline } from '@/features/trade/lib/buildTradeTimeline';
 import { resolveImageUrl } from '@/shared/lib/resolveImageUrl';
-import { createOrGetChatRoom } from '@/features/chat/api/room';
+import { createOrGetChatRoomByTrade } from '@/features/chat/api/room';
 
 const SectionTitle = ({ children }: { children: ReactNode }) => (
   <p className="px-[16px] pt-[24px] pb-[8px] text-[12px] text-[#767676]">{children}</p>
@@ -152,7 +152,7 @@ const TradeDetailPage = () => {
     if (isChatLoading) return;
     setIsChatLoading(true);
     try {
-      const { chatRoomId } = await createOrGetChatRoom(trade.itemId);
+      const { chatRoomId } = await createOrGetChatRoomByTrade(trade.tradeId);
       navigate(`/chat/${chatRoomId}`);
     } finally {
       setIsChatLoading(false);