How do I need a promo code to the form for free entry?

I need to be able to insert a promotion code or something to enable submitting the form with no payment required

I understand that you want to allow your users for a free entry by using a coupon code. As I check your JotForm, I notice that you are using custom calculations and sending the final value to the payment field by 'User defined amount'. Since you are custom calculations, it is required to validate the coupon codes manually using conditions. You may consider adding another text field for entering coupon code and pass the total value to another payment field that needs to be passed to the payment field. Please follow the steps below:

1. Add a textbox field for entering Coupon code

2. Add a new form calculation widget to calculate the final value to be sent to the payment field based on the coupon code.

3. Setup the following conditions to validate the coupon code and calculate the final amount using 'Update/Calculate field' option

4. Change the 'Get Price form' field to the Final Price field in the payment wizard

Please see the screencast below to see how the changes work.

You may take a look at the cloned version of your JotForm below.

https://www.jotform.com/81678318801967

Hope this information helps!