How do I allow a user to input dollar amounts?

We have vendors that prepaid for booth spaces last year.  We want to include an option that allows them to enter the amount they paid, and the number of spaces they paid for.  Prices increased this year, so they will need to pay the difference.  How do I prepare the form to include these details?  I'm at a loss!

You cannot do this with the current payment setup. I would suggest doing the following workaround:

1. Add Dropdown for the items. Label the dropdown with the product name and then add the quantity as the options. You can add a calculation value for the options if you want:

https://www.jotform.com/help/301-How-to-Assign-Calculation-Value

2. Add a textbox that would allow users to input the amount they have paid

3. Add another dropdown that would allow users to select the number of spaces they have paid.

4. Calculate the total using our calculation widget (https://www.jotform.com/help/259-How-to-perform-calculation-in-the-form).

5. Finally, pass the total to the payment field by following the steps in this guide: https://www.jotform.com/help/275-How-to-pass-a-calculation-to-a-payment-field.

When users pay, they will be prompted with just the define description of the payment. You can put a description that would say, Payment for Ordered or Reserved Spaces. 

Please let us know if you need further assistance.