PayPal test mode does not connect

I just connected by form to Paypal Business but when I tried it on the test mode it won't connect; it does connect in the live mode? Why is this?

I also am wondering what is the difference between using the Paypal Business integration and the Paypal Check-out integration and Pay Pay Commerce.

I have a Paypal business account that is connected to a nonprofit

Please take note that a separate account is needed to test PayPal in Sandbox mode.

Guide : How to Test your PayPal Payment Form

Please share to us the URL of your form that have the issue and we will check also.