A card payment appears as 'Failed'. Why is this happening?

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A card transaction may be classed as failed for the following reasons:

There are insufficient funds in the holder's account
The card has expired
The card details are invalid
Fraud prevention algorithms have been applied on the part of the card issuer
The safest way to find out why a transaction failed is to ask your customer to contact their bank or card issuing company and to ask for more information.