9F01

Acquirer Identifier names the acquirer within the broader payment system - a business-layer identifier structurally similar to the Merchant Identifier (9F16, covered earlier) but one level up the hierarchy: 9F16 says which merchant, 9F01 says which acquirer that merchant's transactions ultimately route through. It matters for the same category of downstream, non-cryptographic reasons the other business-context tags in this dictionary matter: settlement routing, scheme-level reporting, and acquirer-specific risk or fee logic all key on this field, none of which the card's own transaction logic reads or depends on. A terminal misconfigured with the wrong 9F01 - most plausibly after an acquirer relationship changes or a terminal is migrated between processors - produces transactions that are otherwise completely valid but that route to, and get reported against, the wrong acquiring relationship entirely, a business-layer error invisible from anything the EMV protocol itself checks. See EMV Contactless Book C-2.