how do I make the credit card fields not required if the charge after coupon is zero?

Hi @stmichaelparish!

You can make the payment field required only to those that need to pay the amount needed. You will need to set up a conditional rule to the payment integration. 

Please use the guide below:

https://www.jotform.com/help/316-How-to-Show-or-Hide-Fields-Base-on-User-s-Answer