When you click on the button you will be able to set your own amount. Just clock on the space for the minimal dollar shown and enter your own amount. It will have a button saying Donate with Paypal. It is misleading as you don’t need a Paypal account so go ahead and click it and select the alternative option for using a credit card (which can also be a debit card).
Just follow the prompts and be sure to read any links or information it as for you to review before you continue. Upon reception of any donations to support this project I tend to leave the funds alone for at least two weeks or more so if there are any issues, or you accidently donate too much, I just go back into that account and hit the refund option to send it back.
In any case, all donations are used for providing this website, the url, keeping it live, any future upgrades and options, as well as for the development needs of the game world environment such as content, servers and so forth. It’s all very specific, very direct and with donations we can keep this all free form needless or excessive third party 'ads.'