When a consumer uses their credit or debit card to make a purchase, the payment processor will identify your merchant bank account using a merchant ID, sometimes referred to as a MID, which is an exclusive identification number granted to your business as a merchant. It can be thought of as the address of your business. Without a merchant ID, the networks involved cannot transmit your money anyplace.

The MID (merchant ID) can help identify a merchant when they connect with their processor and other parties. If a MID was not associated with a transaction, the funds would have no destination. The bank was unable to properly send the money to you.