how can i intergrate a stripe coupon onto my payment form as i have tried and it says the coupon code is not valid

If you are trying to pull a coupon already set up in Stripe, make sure the coupon is properly set up first:

https://stripe.com/docs/recipes/coupons-for-charges

Other coupons can be set up directly in the form:

https://www.jotform.com/help/233-How-To-Add-Coupon-Code-in-the-Payment-Form