acquirer
An acquirer is the regulated firm, licensed by the card schemes, that contracts with a business to accept card payments, routes each transaction to the cardholder's bank, settles the proceeds to the business and carries the obligations to the schemes, including chargebacks and merchant underwriting.
The acquirer sits between the business and the card schemes. It holds the scheme licences, decides whether to take a business on, sets the merchant service charge, receives the authorisation response from the issuing bank and pays the business out after settlement. When a cardholder disputes a payment, the chargeback lands on the acquirer first, which is why acquirers underwrite merchants and hold reserves against risk.
For a software platform, the acquirer is almost never the platform itself. Under a referral model each of the platform's customers signs with the acquirer directly. Under a regulated-partner model the platform's customers are set up as sub-merchants beneath a regulated acquiring partner, which holds the licences and the funds while the platform sets its price. Synapto is not an acquirer and does not hold funds; the regulated acquiring partner does.
For a business, the acquirer is the counterparty on the contract, the name on the settlement and the firm that can hold money back. The PSR found most small merchants do not switch acquirer because prices are hard to compare and contracts roll on, which is what its 2023 remedies on summary boxes and contract terms addressed.