How to prevent duplicate payment submissions?

I got problem with payment many time.

Client made one time payment. But next day charge again , charge again.

I was contact client , she saying made only 1 payment and merchant company check system, not found system error.

I was deleted client form submission, stop problem.

Please check our payment form,,,,,,any problem.

Thank you again.

Sorry for inconvenience this may caused you. 

I am not exactly sure how this has happened. Maybe your user did not closed browser tab in which form was filled and somehow form was resubmitted, most likely by using back browser button.

To prevent duplicate submissions you can set unique submission on your form: 

How to Set Unique Submissions on a Form

You can also set form limit based on unique question:

How to set Form Limits Based on a Unique Question

And you can add a captcha to your form:

How to Add a CAPTCHA field

Let us know if you need further assistance.