diff --git a/tradein-mvp/frontend/src/lib/api.ts b/tradein-mvp/frontend/src/lib/api.ts
index beb34d43..89793996 100644
--- a/tradein-mvp/frontend/src/lib/api.ts
+++ b/tradein-mvp/frontend/src/lib/api.ts
@@ -1,8 +1,11 @@
 import { getOrCreateSessionId } from "@/lib/sessionId";
 
-// Empty default = same-origin relative URLs.
-// In prod Caddy proxies /api/* to backend; in dev Next.js rewrites do the same.
-export const API_BASE_URL = process.env.NEXT_PUBLIC_API_BASE_URL ?? "";
+// При basePath=/trade-in (production behind gendsgn.ru/trade-in/*) API calls
+// должны идти на `/trade-in/api/...`, чтобы Caddy `handle_path /trade-in/api/*`
+// проксировал на tradein-backend — а не в main `handle /api/*` (gendesign).
+// В dev (без basePath) — empty prefix, Next.js rewrites относительный путь.
+const BASE_PATH = process.env.NEXT_PUBLIC_BASE_PATH ?? "";
+export const API_BASE_URL = process.env.NEXT_PUBLIC_API_BASE_URL ?? BASE_PATH;
 
 /**
  * Merges a global X-Session-Id header into the request init.