Friend Cannot Join Server

afternoon y’all, recently me and my friend are hosting a Minecraft Java: 1.21.1 modded server with Fabric.

The Server runs well and everything works for me. I run the terminal, start playit.gg, and can join on my main computer. However, my friend, who lives a couple houses down; when using the IP is always met with “Network Protocol error”. He has already unblocked MC Java from his Firewall and flushed the DNS. Still no outcome.

I’ve checked the server terminal, which only shows that he has “lost connection: disconnects”.
Looking at playit.ggs’ terminal I can see the server is on. (After all, I joined using the same Ip and everything works just fine for me.). However, It does show that my friend “is not using special land address”. It also shows “sent auth request”

We’re both new to this and are used to using Falixnodes and Aternos. Trying to move to something different and more secure in internet than purchasing a server host. Any help would be greatly appreciated. Thank you sm <3