Thank you for reporting this issue and for the positive feedback on the plugin @rojokuze
We need some more information from you; do you mean you have setup 2FA for a super administrator via email, and when you try to login to a sub site with the super administrator account the plugin is not sending the email with the one time code?
If that is the case, then it’s something specific on your website. I just tested it and can confirm that it works in a vanilla install. In that case we need to do some troubleshooting.
For example, can you start by disabling all the other plugins and confirm if it works? If it works with all the other plugins deactivated, start activating the plugins one by one and logout / log back in each time you enable a plugin.
When you do not receive a code, then you can tell with which plugins we might be having a conflict.
Can you please do such test and advise?
Looking forward to hearing from you.