public/static/js/game.js

@@ -410,6 +410,10 @@
                     MapGuesser.showModalWithContent('Error', 'This game is already started, you cannot join.');
                     break;
 
+                case 'game_not_found':
+                    MapGuesser.showModalWithContent('Error', 'The game room was not found by this ID. Please check the link.');
+                    break;
+
                 default:
                     MapGuesser.showModalWithContent('Error', 'Error code: \'' + error + '\'');
                     break

src/Controller/GameController.php

@@ -114,6 +114,11 @@ class GameController
         }
 
         $room = $this->multiRoomRepository->getByRoomId($roomId);
+
+        if(!isset($room)) {
+            return new JsonContent(['error' => 'game_not_found']);
+        }
+
         $state = $room->getStateArray();
         $map = $this->mapRepository->getById($state['mapId']);
         $token = $this->getMultiToken($roomId);