On the machine where you want to share a tmux session with upterm first run:
nix run git+https://upterm.ntd.oneor:
upterm host --server ssh://upterm.ntd.one:2222 --force-command 'tmux attach -t pair-programming' -- tmux new -t pair-programming
This will output something like:
=== YXBRHY1BXARIWTSGXJ8L
Command: tmux new -t pair-programming
Force Command: tmux attach -t pair-programming
Host: ssh://upterm.ntd.one:2222
SSH Session: ssh yXbrhy1bXaRIwTsgxJ8l:Wzo6XToyMjIy@upterm.ntd.one -p 2222
Press enter to continue
Copy the SSH Session url and press enter before sharing the url with your peer.