Error message

I need to switch PayPal accounts -- both are business accounts. The old account was PayPal Pro, the new one is PayPal express.  The form I currently use was created under the old system. I have repeatedly checked, crosschecked & doublechecked the API numbers which I pasted from my database and directly from PayPal.

[PayPal Express Error]

-An error has occurred. Please contact form administrator for assistance.

[Transaction refused because of an invalid argument. See additional error messages for details.]

-You are not signed up to accept payment for digitally delivered goods.

I repeated the set up and, in sandbox mode, got the message:

************

Security error

Security header is not valid

************

As things stand I'm looking for alternatives to JotForms as I've spent two days on this already.

[PayPal Express Error]

-An error has occurred. Please contact form administrator for assistance.

[Transaction refused because of an invalid argument. See additional error messages for details.]

-You are not signed up to accept payment for digitally delivered goods.

The error message you were receiving is relate to your PayPal account. Have you enabled Digital Goods for Express Checkout in your PayPal account?

Please check this guide for more details:

Configuring PayPal Express Integration

Security error

Security header is not valid

The security header is not valid error usually means that there is an issue with provided API credentials.

Please note that PayPal API credentials for Live and Sandbox modes are different.

How to Test your PayPal Payment Form

If I understood correctly, your issue is now resolved. 

I moved your new questions to the separate threads. I will reply to you there shortly:

https://www.jotform.com/answers/1363494 

https://www.jotform.com/answers/1363495