I'm sorry but the only way to donate to the server is via http://store.happy-hg.com/
Nevertheless, if you are having problems with paying, try another payment method, such as credit card/debit card/prepaid card, etc. which don't require to own a PayPal account in order to use!
As I told you in the PM, this isn't a server-side issue, PayPal is rejecting your credit card so there seems to be a problem with it. Try using a different card/payment method or contacting your card providers and ask them what's going on
Read the first time Zainos commented "try another payment method, such as credit card/debit card/prepaid card, etc. which don't require to own a PayPal account in order to use!"