Apart from entering a card number and an expiration date, you probably will have to enter a security code — a feature on every credit card meant to help verify the card is in your possession.

However, American Express cards use a four-digit security code, often called a CID (Card Identification Number), which is located on the front of the card, above the card number. These differences ...

The Card Verification Value (CVV) is a crucial security feature found on credit and debit cards. This three- or four-digit ...