The error message "Gateway error: Credit card number is required" typically means that the payment gateway is not receiving the required credit card information for the transaction to be processed. Here are some things you can try to resolve the issue:
Make sure that the customer's credit card information is entered correctly and completely.
Check the payment gateway settings in your Magento site to ensure that the payment method is properly configured and enabled.
Verify that your payment gateway account is set up properly and has been authorized to process transactions.
Contact your payment gateway provider's support team to troubleshoot the issue further.
You can also try using a different payment method to see if the issue persists, or try using a test credit card to see if it is a problem with the payment gateway or the credit card information itself.
If none of these solutions work, it may be best to contact your payment gateway provider for assistance.
