diff --git a/V2/time_entries/_application/_activities/_create_activity.py b/V2/time_entries/_application/_activities/_create_activity.py
index cb5f5472..c745a1cd 100644
--- a/V2/time_entries/_application/_activities/_create_activity.py
+++ b/V2/time_entries/_application/_activities/_create_activity.py
@@ -25,7 +25,7 @@ def create_activity(req: func.HttpRequest) -> func.HttpResponse:
     validation_errors = _validate_activity(activity_data)
     if validation_errors:
         return func.HttpResponse(
-            body=validation_errors, status_code=400, mimetype="application/json"
+            body=json.dumps(validation_errors), status_code=400, mimetype="application/json"
         )
 
 
@@ -59,4 +59,4 @@ def _validate_activity(activity_data: dict) -> typing.List[str]:
     return [
         f'The {missing_key} key is missing in the input data'
         for missing_key in missing_keys
-    ]
\ No newline at end of file
+    ]