A reference number is a unique identifier assigned to any financial transaction, including those made using a credit or debit card.

An SSN is required to work in the U.S., while an EIN is recommended for all business owners. Foreign-status individuals need an ITIN to do business in the U.S.

A bank identification number (BIN) is the initial set of four to six numbers on a credit card that identifies the lending institution. It helps merchants track transactions.