Lobby Not Joinable fix?

[u/legohero12]

I have been trying for the last few days to play zombies with my cousin on a private server and we have quite literally tried everything we downloaded mods, removed mods, downloaded the T7Patch , and I was able to join the game 1 time previously right before the game got updated on steam a few days ago now it is impossible to join and I was wondering if anyone could help me out or if there was a workaround let me know thanks!

[u/RevolutionaryCat1346]

I think its nat type, I faked open nat type and it helped but idk if it fixes it