Card acquisition is the terminal step that reads before it charges. The terminal polls for whatever the shopper presents, a payment card, a phone, a watch, and reports what it found, including any wallet pass the tap carried, without yet processing a payment. It is the mechanism underneath both tap-based loyalty flows at the till.
The two flows differ in what the acquisition asks for. In one-tap identification, the acquisition carries an amount and polls for the payment method and the pass together; the point of sale learns who the member is, applies their discounts, then completes payment against the already-read card. In two-tap identification, the acquisition polls for the pass alone, and the shopper taps again to pay, with whatever payment method they choose.
The link between the steps is a reference. The acquisition response carries an identifier the point of sale hands back with the payment request, telling the terminal to charge the card it already read instead of asking for a new tap. That reference is what makes one tap genuinely one tap. The pass side of the response carries the member's loyalty identifier, which the point of sale resolves to a profile, a balance and a price list.
One operational detail earns attention: an acquisition that will not lead to a payment must be explicitly closed, or the terminal waits on a transaction that never comes. Point of sale integrations handle this; it is worth knowing because a "frozen terminal" report at the till is more often an unclosed acquisition than broken hardware.