Multiplayer Not Working

[Nepach]

I've scoured the farthest reaches of the internet, and I still haven't found anything similar to my problem. When I gave my brother an invite code, it simply responded with a "Invalid Code", as if it were a random number. And when I try to join a server or host, regardless if it's dedicated or not, it always gives a "Failed to Connect".
I've tried this multiple times, and amongst the troubleshooting I've tried, I have restarted my computer, restarted my router, deleted and reinstalled the game, validated the files, ran it as an administrator, updated my network drivers, and flushed the DNS Cache. The closest I've gotten to a solution, is when I flush the DNS cache, I'm once able to join a dedicated server, before have to quit the game, and re-flush the DNS cache. Even then, the invite codes I give still respond with a "Invalid Code".
I am running on windows, and I think that one more thing that might be giving trouble regarding the invite code, is that my brother is playing on the xbox game pass, and I've read in some of the forums that crossplay is having issues lately.
I hope that this is somewhat helpful

[Rattó]

Invalid code. Are you trying to share mods? If not, then it sounds kinda like a firewall issue. I´m sorry man, I actually have no idea.