cannot connect to my friend's gmod server and any other person can

For some reason I cannot connect to my friend’s gmod server and any other person can.

When I try to connect I get “Connecting to sever” it loads 2 bars then it says “failed to connect after 4 retries”

I’ve tried reinstalling garrys mod, reseting my modem, restarting my computer, verifying the integrity of garrys mod, trying to join through legacy browser and trying to join directly off of my friend.

I can join ANY other server but his for whatever reason thanks in advance

If you have any firewall, try adding an exception for gmod.