diff --git a/src/app/api/v1/stock-purchases/[id]/send-email/route.ts b/src/app/api/v1/stock-purchases/[id]/send-email/route.ts
index f143063..5f1bdac 100644
--- a/src/app/api/v1/stock-purchases/[id]/send-email/route.ts
+++ b/src/app/api/v1/stock-purchases/[id]/send-email/route.ts
@@ -91,7 +91,12 @@ export async function POST(
   const { getAdminPocketBase } = await import("@/lib/server/pocketbase-admin");
   const adminPb = await getAdminPocketBase();
   const pbUrl = process.env.NEXT_PUBLIC_POCKETBASE_URL || process.env.PB_URL || "";
-  const dashboardBaseUrl = req.nextUrl.origin;
+  // Build the callback base URL from DASHBOARD_URL — NOT
+  // `req.nextUrl.origin`. Inside the Next.js process the origin
+  // resolves to the bind address (e.g. `0.0.0.0:3000`), which the
+  // n8n container can't reach. DASHBOARD_URL is the same env var
+  // the customer-PO route uses for this purpose.
+  const dashboardBaseUrl = (process.env.DASHBOARD_URL || "").replace(/\/+$/, "");
 
   if (result.failure) {
     return NextResponse.json(