Error code
Card Network 91
CARD NETWORK91
Payment Decline Code· Why a card payment was declined by the issuer or processor, and what to do.
What it means
Issuer or Switch Inoperative.
How to fix it
- Wait and retry the payment.
- if the problem persists try a different card.
Not affiliated with Card Network. Answer summarized from the manufacturer's manual linked above; consult that source for the authoritative procedure.