Can I set up a coupon where the registrant fills out the amount of the coupon themselves?

We want to sell a gift certificate in varying amounts in a different form. The person who is gifted the certificate will use our general registration form - link below. They will need to put in how much they received as a gift and deduct that from the balance that they owe. Can this be done with a coupon? 

I assume you would like to have a custom field where your users can enter their coupon which will deduct the price of the total price.

I'm afraid that is not possible through the existing payment integration, but it might be possible with regular fields.

What I mean is, you can use regular fields to represent products and coupons:

Coupon value field which will be read-only will hold the value of the coupon so it can be deducted from the actual price:

And payment field will have to be adjusted as well:

And this is how it works:

You can check my form as well: https://form.jotform.com/73316242651956

Of course, this will work if you don't have a lot of coupons since it will require creating each condition separately.

Hope it helps.

Thank you!