diff --git a/api/utils/api_utils.py b/api/utils/api_utils.py
index 9b0b481e3..30cf12aae 100644
--- a/api/utils/api_utils.py
+++ b/api/utils/api_utils.py
@@ -56,6 +56,30 @@ from rag.utils.mcp_tool_call_conn import MCPToolCallSession, close_multiple_mcp_
 
 requests.models.complexjson.dumps = functools.partial(json.dumps, cls=CustomJSONEncoder)
 
+def serialize_for_json(obj):
+    """
+    Recursively serialize objects to make them JSON serializable.
+    Handles ModelMetaclass and other non-serializable objects.
+    """
+    if hasattr(obj, '__dict__'):
+        # For objects with __dict__, try to serialize their attributes
+        try:
+            return {key: serialize_for_json(value) for key, value in obj.__dict__.items() 
+                   if not key.startswith('_')}
+        except (AttributeError, TypeError):
+            return str(obj)
+    elif hasattr(obj, '__name__'):
+        # For classes and metaclasses, return their name
+        return f"<{obj.__module__}.{obj.__name__}>" if hasattr(obj, '__module__') else f"<{obj.__name__}>"
+    elif isinstance(obj, (list, tuple)):
+        return [serialize_for_json(item) for item in obj]
+    elif isinstance(obj, dict):
+        return {key: serialize_for_json(value) for key, value in obj.items()}
+    elif isinstance(obj, (str, int, float, bool)) or obj is None:
+        return obj
+    else:
+        # Fallback: convert to string representation
+        return str(obj)
 
 def request(**kwargs):
     sess = requests.Session()
@@ -128,7 +152,11 @@ def server_error_response(e):
     except BaseException:
         pass
     if len(e.args) > 1:
-        return get_json_result(code=settings.RetCode.EXCEPTION_ERROR, message=repr(e.args[0]), data=e.args[1])
+        try:
+            serialized_data = serialize_for_json(e.args[1])
+            return get_json_result(code= settings.RetCode.EXCEPTION_ERROR, message=repr(e.args[0]), data=serialized_data)
+        except Exception:
+            return get_json_result(code=settings.RetCode.EXCEPTION_ERROR, message=repr(e.args[0]), data=None)
     if repr(e).find("index_not_found_exception") >= 0:
         return get_json_result(code=settings.RetCode.EXCEPTION_ERROR, message="No chunk found, please upload file and parse it.")