diff --git a/backend/app/services/video_renderer.py b/backend/app/services/video_renderer.py
index 48fe9c3..f64975b 100644
--- a/backend/app/services/video_renderer.py
+++ b/backend/app/services/video_renderer.py
@@ -174,7 +174,7 @@ class VideoRendererService:
 
         response = client.post(
             f"{service_url}/probe",
-            json={"source_gcs_uri": gcs_uri},
+            json={"gcs_uri": gcs_uri},  # Matches ProbeRequest model
             headers={"Authorization": f"Bearer {auth_token}"}
         )
         response.raise_for_status()