I think this is probably a question for PayPal, then, and not for MeepCraft. I'll do my best to help, though!
First, you'll want to do what it tells you in the screenshot - check your PayPal account carefully for any recent transactions and check the e-mail account associated with it for any receipts that say you paid. If you find nothing, that means the payment did not go through, and you just need to try donating again. :) If it keeps happening, you'll need to contact PayPal customer support to try to fix the issue.
