What does the error message "Gateway authentication failed" mean?

If a merchant sees the error message"Gateway authentication failed" when trying to do a transaction, it means there is a problem with the merchant credentials (merchant identifier and merchant secret key).

Verify the merchant the merchant credentials in your backend. You can create a new merchant secret key in the Gateway Manager (see here).

Make sure to kill the app and start it again, after you adjusted the merchant credentials in your backend, to prevent any problems with caching.