with ?listen as Options 
When you are testing a game you should use 480 or your own and when you publish the game use your own id, or else you will get banned by Steam. The 480 id will not affect your testing, people from your country will still be able to join and test.
The fix wasn’t that you used server travel. ServerTravel and Open Level are ways to change the level and how it is done in the background. The plugin you are using is expecting you to use ?listen.