diff --git a/.claude/settings.local.json b/.claude/settings.local.json
index 8c05482..3afad14 100644
--- a/.claude/settings.local.json
+++ b/.claude/settings.local.json
@@ -63,7 +63,8 @@
       "Bash(git show *)",
       "Bash(git status *)",
       "Bash(git revert *)",
-      "Bash(git commit -m 'Fix price display issues and layout in design review page *)"
+      "Bash(git commit -m 'Fix price display issues and layout in design review page *)",
+      "Bash(git commit -m 'Fix: Calculate effectivePrice in design API endpoints *)"
     ]
   }
 }
diff --git a/src/app/api/designs/[id]/approve/route.ts b/src/app/api/designs/[id]/approve/route.ts
index 3caee91..e0ed3e4 100644
--- a/src/app/api/designs/[id]/approve/route.ts
+++ b/src/app/api/designs/[id]/approve/route.ts
@@ -1,6 +1,7 @@
 import { NextResponse } from 'next/server';
 import { prisma } from '@/lib/prisma';
 import { sendDesignApprovedEmail } from '@/lib/mail';
+import { toProductDTO } from '@/lib/product';
 
 export async function POST(
   req: Request,
@@ -30,7 +31,10 @@ export async function POST(
       checkoutLink,
     });
 
-    return NextResponse.json(updated);
+    return NextResponse.json({
+      ...updated,
+      product: toProductDTO(updated.product),
+    });
   } catch (err) {
     console.error('Error approving design:', err);
     return NextResponse.json(
diff --git a/src/app/api/designs/[id]/route.ts b/src/app/api/designs/[id]/route.ts
index b240fd2..77ac59c 100644
--- a/src/app/api/designs/[id]/route.ts
+++ b/src/app/api/designs/[id]/route.ts
@@ -1,6 +1,7 @@
 import { NextResponse } from 'next/server';
 import { prisma } from '@/lib/prisma';
 import { getCurrentCustomer } from '@/lib/auth';
+import { toProductDTO } from '@/lib/product';
 
 export async function GET(
   req: Request,
@@ -16,7 +17,10 @@ export async function GET(
       return NextResponse.json({ error: 'Design not found' }, { status: 404 });
     }
 
-    return NextResponse.json(design);
+    return NextResponse.json({
+      ...design,
+      product: toProductDTO(design.product),
+    });
   } catch (err) {
     console.error('Error fetching design:', err);
     return NextResponse.json(
@@ -44,7 +48,10 @@ export async function PATCH(
       include: { product: true, messages: { orderBy: { createdAt: 'asc' } } },
     });
 
-    return NextResponse.json(updated);
+    return NextResponse.json({
+      ...updated,
+      product: toProductDTO(updated.product),
+    });
   } catch (err) {
     console.error('Error updating design:', err);
     return NextResponse.json(