I want to add a discount code to a membership Form.

Essentially I want a txtfield that can take a text entry for a discount code. And either when they enter this code or press a apply button the discount coded is added (or discounted) to the Amount total which has already been populated from a radio button. 

Either way is fine 1. push a button to apply discount or 2. have the discount code checked when cursor leaves field 

and if a good code was entered apply the discount.

So if they enter "Welcome2022" in the field they get a discount applied of $10 off.

SW