Most "I tried to buy credits and something's wrong" issues fall into one of two scenarios.
The page froze, or you got charged but no credits appeared
This usually means the payment didn't actually complete on our side, even though your bank or PayPal showed a temporary charge. In most cases the charge reverses on its own within a few days because the funds were never captured. Wait it out and the pending charge should disappear from your statement.
If after a few days the charge has cleared (it's no longer pending) but you still don't have the credits, open a support ticket and include the date, amount, and last 4 digits of the card (or PayPal email). We'll match it to a transaction and sort it out.
The transaction got declined
Declines come from Braintree (owned by PayPal), and we can't override their decisions. Usually means the bank or PayPal flagged the payment. Try one of the alternatives: