JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
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Please refer also to our user guide: How-To-Add-Coupon-Code-in-the-Payment-Form
You need to open again the payment tool configuration wizard by clicking that magic wand like icon.
and then just updated the options in the Coupon code i.e. in this case your 'Coupon Limit' option.
Hope this help. Let us know if you need further assistance.