Don't worry! It happens sometimes. Transactions can fail for several reasons. Sometimes you can guess why it was declined based on the response code, but only your credit card issuer or financial institution can confirm the specific reason, so your best bet is to get in touch with them.
These are the usual culprits for credit cards:
Incorrect credit card number or expiration date
Insufficient funds
If you see a message that says “Processor Network Unavailable,” it could indicate a glitch with the back-end processing network. Try the transaction again.
These are the usual culprits for PayPal payments:
If you see a message that says “Processor Network Unavailable,” it could be a glitch in the back-end processing network. Try the transaction again!
If you see a message that says “Paypal Pending payments are not supported,” then reach out to PayPal and ask them not to put payments on review.