Some European credit card companies use something called a “issue number,” but MasterCard does not. If a MasterCard issue number is asked for at an online checkout, it can be left blank or the number 0 can be used.
Some online stores in Europe need you to enter an issue number. Issue numbers are not used on most credit cards, including MasterCard. Depending on the store, the transaction can be finished either by leaving the field blank or by typing the number 0. In the UK and Europe, debit cards are more likely to have an issue number. Most Americans don’t know what the term “issue number” means when it comes to credit card transactions.