Hey, thank you for reaching out.
As for now you need to have at least PHP 8.0.15 running on your server.
Yes, you have the possibility for LNURL Auth only on your wp-login.php page.
At the moment it's not possible to charge a fee to use LNURL Auth. I will check this out. Thank you for the input.
Anyway, if you notice a spammer, you have the possibility to ban the account by copy-pasting the linkingKey from the user edit screen to the banlist in the plugin settings page.