The Footballguys Merch Store uses Shopify for checkout. They accept cards from Amex, Visa, Mastercard, Discover, JCB, Diners Club, and Elo, as well as payments from Apple Pay, Facebook Pay, and Shop Pay.
If you are not using one of those payment options, or you are and for some reason, it is not working, you will need to contact your bank or Shopify about the issue. The process is fully handled by Shopify, and there is nothing that Footballguys or Footballguys Customer Service can do to help or troubleshoot the issue.