I'm using PayPal Payments Advanced and I am receiving an error when clicking the button "Place Order" on my one page checkout. The error is "User Authentication Failed". I have confirmed my credentials in Magento for PayPal. I have gone over the steps provided by both PayPal and Magento for integration multiple times, but have been unable to proceed past this error.
I have tried various solutions for Google, such as updating the Cancel, Error and Return URLs on Manager.PayPal.com, but with no success.