I get this error when testing donations, the result is the same in test and live environments. "Error Payment approval failed with message :Security error Security header is not valid" I searched every forum out there and tried every solution I could find with the same result every time.
I checked the name, key, and secret 1000 times and then reset it and again tried 100 times.
I tried using the login name as suggested on a forum and that did not help.
I removed the payment option and re-added it.
I tried the test variables in the live settings via your forum and no go...
I tried this and it came back ok so I assume paypal works (Info changed 4 security) "https://api-3t.paypal.com/nvp?&user=info_api1.rockymountainmustang.org&pwd=JPJUK7LxxxxxYLR&signature=A.MRLXfmAocfnxxxxxRHc67jlS52IYYS7LRw&version=70.0&METHOD=SetExpressCheckout&RETURNURL=http://www.paypal.com/test.php&CANCELURL=http://www.paypal.com/test.php&PAYMENTACTION=Sale&AMT=50&CURRENCYCODE=USD"