diff --git a/fedn/network/api/v1/session_routes.py b/fedn/network/api/v1/session_routes.py
index a045e60bf..9158b47df 100644
--- a/fedn/network/api/v1/session_routes.py
+++ b/fedn/network/api/v1/session_routes.py
@@ -393,7 +393,7 @@ def start_session():
         min_clients = session_config["clients_required"]
 
         if control.state() == ReducerState.monitoring:
-            return jsonify({"message": "A session is already running."})
+            return jsonify({"message": "A session is already running!"}), 400
 
         if not rounds or not isinstance(rounds, int):
             rounds = session_config["rounds"]
@@ -410,6 +410,7 @@ def start_session():
     except Exception:
         return jsonify({"message": "An unexpected error occurred"}), 500
 
+
 @bp.route("/<string:id>", methods=["PATCH"])
 @jwt_auth_required(role="admin")
 def patch_session(id: str):