Secure Credit Cards uses a checksum (Luhn algorithm) to confirm that a valid card number is entered. If the checksum fails, because a digit is incorrect, missing, transposed, etc. an error reports, "Invalid Card Number". This Solution describes this feature. (6197)
Secure Credit Cards uses a checksum to ensure a valid card number is entered. If the checksum fails, an error reports, "Invalid Card Number". Any transcription error such as missing, incorrect, or transposed digits can cause the checksum to fail.
This feature provides some assurance, if the checksum succeeds and there is no error, that the card number has been transcribed correctly. It is important to note that this does not ensure that the card number is correct, active, or, for that matter, real.
For example, and for testing purposes, the account number, 4111-1111-1111-1111, can be used and the checksum will succeed even though it is not a real card number.