If you try processing a SNAP transaction, and you see this error, there may be an issue with your FNS number. Contact WorldPay at 1-800-859-5965 option 9 extension 1926. Inform them that you are getting this error type, and they will be happy to assist you.
The WorldPay Help Desk can be reached 24/7, and they handle all issues that occur with transactions. If your transactions are denied because of an Error 05: Unauthorized Usage, then WorldPay Help Desk is the correct contact.