Update app.py

app.py

@@ -104,8 +104,13 @@ async def get_track_download_url(track_id: str) -> str:
 async def track_dl():
     track_id = request.json.get('track_id')
     dl_url = await get_track_download_url(track_id)
-    result = {"url": dl_url}
-    return jsonify(result)
+    if dl_url:
+        result = {"url": dl_url}
+        return jsonify(result)
+    else:
+        result = {"error": "failed to fetch the track"}
+        return jsonify(result)
+