I have installed paypal express on zen cart 1.3.9.
When I click on the paypal button, I get this error message.
We are sorry for the inconvenience. The PayPal account authentication settings are not yet set up, or the API security information is incorrect. We are unable to complete your transaction. Please notify the store owner so they can correct this problem. (10002) 10002 Security error - Security header is not valid
I have read the help me files but have not anything on authentication settings.
I have tripled checked the API settings(user name, password, api password, signature, etc..) and they are correct.
I'm not sure what the authentication settings are?