When I click Checkout using the PayPal payment option in my online shop, I receive this error message:
PayPal has returned an error!
Correlation ID: 81f242f06f3ec
Error Number: 10002
Short Message: Security error
Long Message: Security header is not valid
You'll get this error if there is a problem with your PayPal account. Double-check that you have added the correct API username, password, and signature under the Payment tab. It would also be a good idea to log into your PayPal account and verify that it is active.