How to add a place to add a tip on my Stripe payment form?

I would like to add a place to add a customer tip on my Stripe payment form but do not know how to go about doing this - Here's a link to my Stripe payment form https://form.jotformpro.com/71758047084967

Your help is GREATLY appreciated - thank you so much!

You need to use the "Sell Products" payment type and create 2 products.

Product 1 - Service or Labor Fee = $20
Product 2 - Tip = $1

You need to add an option in the 2nd product. Please click the "Add" button in the Add a Quantity Selector option.

You can use the "Text Box" option with a Default Quantity of 1.

Here's a demo form: https://form.jotform.com/80607515324957

Here's a guide: https://www.jotform.com/help/225-How-to-Add-Options-to-Payment-Forms.

Result:

Hope that helps. If you have any questions, let us know. Thank you.

The customer has to enter their invoice amount and so one of the options has to be PAYMENT TYPE: user defined amount.

If you would like to make use of a user defined amount, your solution shall be using the regular fields for your form and with using a form calculation widget in order to perform calculations on your form. 

Here is a quick guide that you can refer to for information on using this method: https://www.jotform.com/help/259-How-to-Perform-Form-Calculation-Using-a-Widget

Feel free to let us know if you have additional questions.