The expiration input field requires that you enter the expiration date in the format MM/YY and you have to manually add the '/' yourself.

The most common reasons you will receive this error message is if you did not manually enter the '/' or if you attempted to add the full year, or added the day also.

Try re-entering your expiration date with the '/' in the following format: MM/YY

If you continue to experience issues, please contact support so they can investigate further.