I accidentally completed and incomplete payment, did it charge the customer?

I accidentally completed a form payment for one of our guests, and I need to refund it ASAP.

If there was an incomplete payment submission:

https://www.jotform.com/help/564-how-to-view-incomplete-payments-of-your-payment-forms/

And you manually completed it, it will not charge them.  Completing an incomplete payment only places the data in with the rest of your submission data and marks it as complete.  It does not do anything on the payment processing side. 

If the payment was not completed when the form was first submitted, it is actually not possible to charge them.