Someone was able to submit the form without the required payment

Hello, someone was able to submit registration form info without filling out and paying with the required credit card checkout section of the form.

When i go to this particular submission, there is no checkout section like it was just skipped, even though it is required.

What could be the cause of this?

Please provide us the ID of the form and the ID of the submission where required data is missing. 

In case that the form is embedded, please provide us the webpage URL.

Looking forward to your reply.

I suspect that the payment validation has failed to work for the user allowing him to submit the form without the payment. This is a rare case in our forms. If you may, I would suggest asking the user about it. Ask him if he has provided the card details in the form and if he is charged somehow. Otherwise, ask him to re-submit the form to process the payment. 

Thank you for the information. I will proceed as recommended.
If he somehow charged however, there will be a problem because we didn't
get his money.
I highly doubt this though.
...

Everything is fine, he was not charged.
Thank you.
...