Decline code 51 (insufficient funds): what it means at the terminal

Decline code 51 means the card's bank declined because there are not enough funds, or the sale would go over the credit limit. The terminal is working; the customer needs another payment method, a smaller amount, or to add funds.

Before you start

• Check the code is 51 or the words Insufficient funds. Other codes have other fixes.
• Check the amount. A mistyped amount is the one cause you can fix at the terminal.

Steps

1. Confirm the screen or declined receipt shows 51 or Insufficient funds. Expected: you know the bank declined for lack of funds or credit.
2. Check the amount you entered. Expected: a keying mistake is caught and the sale is re-entered for the right amount.
3. Do not complete the sale or re-run the same card again and again for the same amount. Expected: nothing leaves unpaid. Visa's dispute guide says a sale completed after a decline can be charged back.
4. Tell the customer privately that the bank declined for insufficient funds and ask for another card or payment method, or a smaller purchase. Expected: the sale completes another way.
5. If the customer adds funds or the bank raises the limit, run the sale again as a new transaction. Expected: approval.

If that did not work

A 51 on one card is between the cardholder and their bank. If many cards decline with 51 for normal amounts, check the amounts the terminal is sending and contact Allstar support with the model, serial number, payment application, processor and the exact message on screen.

Sources

• Adyen Docs: Raw responses
• Adyen Docs: Mapping to Visa system integrity fee categories
• Worldpay Developer: Raw response codes
• Mastercard Developers: Network Response Codes
• Visa Dispute Management Guide for Merchants (October 2026)