I tried entering fake credit card information in the registration system of an online newspaper to be able to read an article. The first few tries were not accepted. Then I found another website which generates fake credit card information. Using the information from this particular website worked.
I am pretty sure the credit card number is not charged because the first one month of the subscription was free.
Now, my question is, how did my last try succeed although he first two tries got rejected by the system? I thought the system checks whether all the entered information is valid, i.e.: First Name, Last Name, Security Number on the back of the credit card, expiration date and the credit card number have to be valid and match together.
How is the validation/verification test done by the system? Do all systems do it in the same way or do they differ?