Scene created from a script gives an error when tried to load

So I have made a script that makes a scene from a script and then loads it but for some reason I get this error:

and here is the script:

SceneManager.CreateScene("Floor" + GameManager_RoomCount.gameManagerRoomCount.floor);
            SceneManager.UnloadScene("Floor" + (GameManager_RoomCount.gameManagerRoomCount.floor - 1));
            SceneManager.LoadScene("Floor" + GameManager_RoomCount.gameManagerRoomCount.floor, LoadSceneMode.Single);

(I have imported scene management)

The script makes the next scene, unloads the current scene then loads the scene that has just been created. I don’t know why it is giving me an error.

To use LoadScene, the scene must be included in the build settings as documented. Have you tried SetActiveScene?