Quick answer: A merchant category code (MCC) is a four-digit number that tells card networks and banks what your business sells. Visa and Mastercard treat a small group of MCCs as high-risk, including 5967 (inbound teleservices, used for adult content), 7995 (gambling) and 6051 (quasi-cash, including crypto). If your business falls into one of them, you need extra registration, you pay higher fees and issuers decline more of your transactions. Using the wrong MCC to avoid thi