We don't receive much information from credit card companies or PayPal as to why cards/Paypal accounts decline.
The most common reasons are insufficient funds, mis-entered payment details, or in some cases, the issuing bank has blocked the charge. You'll want to reach out to your bank or PayPal directly to make sure everything is accurate and whitelisted from being blocked as a charge.
We automatically retry declined payments, so if your payment method is in good standing, you will receive another email notifying you of a successful charge within a day or two. If you'd like to speed up the process, you also have the option of clicking "retry" from your payment methods once you update your payment details.
You can also add a new payment method if your existing info doesn't work, you can get more instructions here.