Try exiting it and then make sure no tmux process is still running, by for example running ps -aux | grep tmux.
For future reference: the command to kill the tmux daemon (and as a side-effect, all other running tmux processes connected to it) is tmux kill-server
(or in tmux, typing <prefix> :kill-server
, assuming default keybindings).
No idea about the Lemmy hosting bit, but I highly doubt that .com you got will renew at $1 going forward. Judging by this list it’ll most likely be $9+ after the first year.
At $1/year, the registrar you used is taking a loss because they pay more than that to the registry for it. They might be fine with that for the first year to get you in the door, but they’d presumably prefer to be profitable in the long term.