Player count problem

I made a server for a friend and I to play on and even changed the time zone (since we both live in completely different places) but for some reason, he can't join since it would say "unable to connect to world."

I did everything I could to fix this like changing the max players from two to 20 and the allow list thing (yes I'm positive of his gamer tag) but the server would still not let him connect. Also, when I try to join the server, the slots would say "0/1" in the players section so that was kind of fishy.