MyBB Community Forums

I want to put an upgrade page on my site where users can pay to upgrade to usergroups they purchase

any plugins/

such plugins might not be available freely.
you can try using this method => Link

you can use mysubscriptions

here is and upgrade page template if you want to use
https://anonshare.eu/Thread-Theme-upgrade-page
preview here
https://anonshare.eu/upgrade.php

Yeah many users use the my subscriptions plugin.

There is a paid and a free version you can use the most usefull for you.

But in both versions you will need to customize and set up your upgrade page as all those users who have it already done