Get Help With Toast Error: Credit Card Number Should be 16 Characters

How would I troubleshoot the "Credit card number should be 16 characters" error?

This error message occurs when you enter an invalid credit card number. Visa, Mastercard, and Discover credit cards have 16 digits, while American Express credit cards only have 15 digits. However, this error implies that the inputted credit card number is not valid for any of the four processors.

Enter a valid credit card number with no spaces or dashes to fix this error.