How does money actually move in an account-to-account payment?

What the scheme does not do is tell the merchant which sale was paid, at which till, and what to do next. That part has to be built on the merchant side, at the merchant's bank. This article draws a simple map of the parties, the messages between them, and the point where the scheme's work ends and acceptance begins.

The four parties and what each one owns

The payer and their banking app. The payer authorises the payment with a PIN or biometrics. Nothing moves until they do.
The payer's bank. It checks the balance, debits the account and sends the transfer into the scheme.
The scheme, or instant payment system. It owns the rulebook and the switch that routes messages between banks. In Moldova this is MIA, built by the National Bank of Moldova and launched in March 2024¹. Romania's RoPay, run by the national clearing house, went live in October 2024². In the euro area, the Instant Payments Regulation requires funds to reach the payee's account within ten seconds of the payer's bank receiving the payment order³.
The merchant's bank. It receives the transfer and credits the merchant. It holds the licence, the scheme membership and the merchant relationship. In industry terms, this bank is the A2A acquirer.

Every payment needs three things: messaging (the instruction from bank to bank), clearing (working out what each bank owes the others) and settlement (money actually moving between the banks). A batch system does these in groups during business hours; standard ACH in the United States settles the next business day⁴. An instant system does them for each payment individually. The BIS defines a fast payment as one where the message and the availability of final funds to the payee happen in real time or near real time, as close to 24/7 as possible⁵. Settlement arrangements differ between schemes, but from the merchant's seat the money is there in seconds.

Where the scheme's work ends

From the scheme's point of view the payment is complete once the merchant's bank has the credit. From the merchant's point of view several questions are still open: which order this was, which till took it, which shift it belongs to, and how to refund it if the customer comes back.

Answering them is the job of acceptance, which sits on top of the scheme:

presenting the request: a payload (QR code, payment link, NFC tag) or a request-to-pay, where the scheme supports it;
matching the incoming credit to the sale that created the request;
telling the till, the online shop or the chat that the sale is paid;
refunds, which on a push rail are a new payment back and depend on what the scheme allows;
reconciling the day and closing the shift.

For cards, the acquirer sells this layer as one package. On instant rails it is being built market by market. The rails are ready. The checkout is not.

The messages, in order

On the ISO 20022-native rails miaPOS supports (SEPA Instant, MIA and RoPay), a payment uses a small set of messages:

The request. The merchant side creates a payment request with an amount, the payee and a reference. If it is a QR code or link, the payer's app reads it directly. As a request-to-pay, it travels to the payer's bank as a pain.013 message, on schemes that support it.
The transfer. After the payer approves, the payer's bank sends a pacs.008 credit transfer through the scheme to the merchant's bank.
The notification. The merchant's bank reports the credit to its customer, for example as a camt.054 notification.

Acceptance software turns these bank messages into what the merchant's systems need: "paid" on the terminal screen, a callback to the online shop's backend, a line in the merchant back office and a Z report at the end of the shift. Confirmation is covered in more detail in How does a checkout learn that an A2A payment is confirmed?.

Where miaPOS sits

miaPOS is acceptance software inside the bank's perimeter. Your licence, your regulator, your relationship: the bank keeps all three, and miaPOS works with the scheme the bank's regulator recognises. On the map above, it sits between the merchant and the merchant's bank. It generates the payment request, receives the confirmation and runs the merchant back office, where transactions from the terminal, the online checkout, payment links and chat land in one place.

The funds go straight from the payer's bank, through the scheme, to the merchant's account at the bank. miaPOS handles the messages around them. For a bank's product team, this means the scheme connection and the merchant relationship stay where they are, and the acceptance layer is what gets added. The roles are set out in full on What is A2A acquiring?.

Common questions

What is the difference between the scheme and the acquirer in an A2A payment?

The scheme owns the rules and routes the transfer between the payer's bank and the merchant's bank. The acquirer is the merchant's bank: it holds the licence and the scheme membership, signs up the merchant and credits the merchant's account. Acceptance software works for the acquirer, on the merchant side.

Does the money pass through the acceptance software in an A2A payment?

No. The funds move from the payer's bank through the scheme to the merchant's account at the merchant's bank. Acceptance software such as miaPOS creates the payment request, receives the confirmation and records the transaction for the merchant.

Which ISO 20022 messages appear in an instant account-to-account payment?

The core one is pacs.008, the credit transfer between the banks. Where the scheme supports request-to-pay, the request reaches the payer's bank as pain.013. The merchant's bank can report the incoming credit as camt.054. Which messages a given scheme uses depends on its rulebook.

A2A acquiring with miaPOS

Building instant-payment acceptance with your merchants? See how miaPOS works with banks.

For banks

Sources

Written by Ghenadie Cernei, Founder, Finergy. 31 October 2026.

How does money actually move in an account-to-account payment?

The four parties and what each one owns

Where the scheme's work ends

The messages, in order

Where miaPOS sits

Common questions

Sources

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