Mystic Cybersource Error Message

• "UsernameToken authentication failed" - that means you might have a invalid SOAP key. In our case, I had a few extra line breaks in the key. 
• "Merchant password has expired" - the SOAP key has expired

NOTE: Cybersource has 3 different security keys, one for Security Acceptance (SA key), one for Silent Order Post (SOP key) and one for SOAP (SOAP key). Make sure you generate the right one to replace your old key!