Unable to use PayPal sandbox

the submit button takes me to PayPal but I cannot get past the login screen.

When you are using the PayPal payment field in Sandbox Mode, it does not make any actual payment - it redirect you to a sandbox environment on PayPal, so that you can simply test out whether your form is otherwise working as expected.

The following guide describes ways for testing out a PayPal payment form:

https://www.jotform.com/help/390-How-to-Test-Paypal-Payment-Form

Please let us know whether there is anything else we can do to help. Thank you.