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My Chase Sapphire has both the CC and CVV numbers on the back.

My AmEx cards have a 3 digit CVV seeming number on the back in addition to the four digit one on the front.

We used to have lots of failed transactions until we explained to users that the CVV on an Amex is the 4-digit number on the front.

But why does Amex does it differently with their 4 digit CVV? Goolge search doesn't reveal any good answer. Thats a big confusion. Anyway cards could have put CVV beside the number if they wanted. In that case I think people would have found them.

Confusingly Amex has both a 4 digit CID (Front) and 3 digit CSC (Back). The latter I think is only ever used internally by Amex, not for transaction processing.

Different systems which use different fraud algorithms proposed by different people from the other credit card issuers.

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