Error code
Card Network 51
CARD NETWORK51
Payment Decline Code· Why a card payment was declined by the issuer or processor, and what to do.
What it means
Insufficient Funds.
How to fix it
- Ask the customer to use a different card or add funds.
- the customer can contact their bank.
Not affiliated with Card Network. Answer summarized from the manufacturer's manual linked above; consult that source for the authoritative procedure.