This is an issue with your credit card and our processing platform - Braintree.
After the 'gateway rejected: AVS error" message there should be a little letter in brackets. The letter in brackets explains the reason for the error.
Here is a complete list of the AVS errors with their corresponding letter explaining the issue; https://developers.braintreepayments.com/reference/general/processor-responses/avs-cvv-responses#avs
If you can not find a solution on the list of errors, please email email@example.com and someone will be in touch with you ASAP.