Yes, but this still does not mean the web form is to blame, nor will a screenshot tell you the root cause of the problem, 99.9% of the time the numbers are fed directly to the payment processor, so it's not like there's anything to mess up.
This is why I suggested calling the card company, because they have the ability to see what went wrong and they will be able to tell you.
This is a fair point, and thanks for the advice, but the form warns you before submitting[0], so I doubt it is actually contacting the payment processor. Anyway, I can't be bothered since the card works everywhere else.
0: and I don't recall, but it may not let you submit.
This is why I suggested calling the card company, because they have the ability to see what went wrong and they will be able to tell you.