A UC decline code occurs when you try and refund a credit card for more than you have originally charged it within the last 12 months. For example, refunding a customer $100 when the original charge was only $50. Charging a customer's Visa credit card $100 but issuing a $100 refund to their MasterCard is another example.
Refunding a credit card for more than you charged violates card association rules.
If you've yet to batch the day's transactions, please edit or void the original charge instead of issuing a refund.
These types of refunds expose your business to risk as a customer may dispute the charge to his Visa, and keep the refund to his MasterCard (thereby double dipping).
A significant number of typos are caught by preventing refunds of this nature.
If you need to issue a refund, and you are receiving a UC error message, you may contact a PayJunction Level 2 representative who may authorize a one-time exception (for example, merchants who have recently switched to PayJunction from a previous provider may still need to refund an older transaction).
Contact PayJunction support for further assistance if you still have questions about what is a UC.