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I get a warning when enter my client's credit card into my software- it keeps saying "invalid card number". On investigation it turns out that the number is weird, in that it does not satisfy the Luhn Algorithm.

(For those of you who don't know what the Luhn Algorithm is, the number on your credit card is not just random digits, it actually has a particular property, where if you add and multiple various digits together you should get a total divisible by 10. If you don't you can tell the card is invalid. Explanation here.)

Should I try to override this warning? My client swears that their bank says the card is valid.

Should I try to contact their bank on their behalf?

closed as off-topic by Nathan L, Joe, quid, JoeTaxpayer Feb 14 '17 at 22:36

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    "but their bank says its valid" Did they tell you than or your client that? I would definitely contact the issuing bank if you suspect fraud. – D Stanley Feb 14 '17 at 16:35
  • You're right- it was my client. I really don't want to believe it is fraud, but I can't see any other explanation. – Urbycoz Feb 14 '17 at 16:41
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    You can call up the bank and ask why it doesn't work. That way you don't have to accuse anyone. You can also ask the client to wire the money to you. – SMeznaric Feb 14 '17 at 16:46
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    Charging a client's credit card doesn't meet my narrow definition of personal finance. – Nathan L Feb 14 '17 at 17:12
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    Thanks for all your comments and advice. Turns out that the number they dictated to me over the phone (that they were so adamant was correct) was not actually being read directly off the card- they were reading the number someone had written down for them. I've told them to check the card itself....and I haven't heard back. So I guess it was their error. – Urbycoz Feb 15 '17 at 11:13
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This sounds like a case of "garbage in, garbage out". Or to put it another way, the problem is between your client's keyboard and his chair.

If the Luhn check is failing, you are entering an incorrect credit card number. Really. Someone has typed it incorrectly, misspelled it, transposed a number, who knows?

Have him send you a photo of the credit card and verify each digit. There's something off.

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    I would note that in order to be PCI compliant, your client would have to send the picture through a secure and encrypted method. You would also have to ensure that it is properly deleted once you're done. security.stackexchange.com/questions/18240/… – Michael Feb 14 '17 at 18:36
  • @DStanley I agree with you, however, regardless of the situation or context, an image of the credit card is being sent. – Michael Feb 14 '17 at 20:19
  • OK I see your point now. Comment deleted. – D Stanley Feb 14 '17 at 20:38
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    @Rocky Seems you were dead right- the card number wasn't actually the one on the card. I just didn't know whether the Luhn check was gospel. Seems it is. – Urbycoz Feb 15 '17 at 11:32

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