In case you want to make a recurring monthly donation, after your innitial month, there is a simple way to do it by using the Donate (https://l2jmobius.org/donate.php) button.
Just make sure you have selected the "Monthly" option.
(https://i.ibb.co/TWfSFCz/image.png) (https://ibb.co/z6MY0kK)