User's credit card rejected on form

A user contacted me after trying to use the form I created to  register for our event. Our form only allows a person to register for one user at a time. He registered and paid for his registration using the form. After successfully his own registration, he went back to the form to register an additional person, but his card was rejected. Why would that happen? Is this a question I need to ask Stripe?

Hello,

Is there any error shown after the card was rejected? We would appreciate if you could provide details on the error so we can further check and investigate this issue.

Also just to clarify, is he using the same card when registering the second user? So the first payment went through and the second did not?

We'll look forward to your reply.

You can disregard this and remove the question. The issue was with his bank. It's been resolved.

Thanks!