Payment processing refers to the sequence of technical and financial operations that transfer funds from a customer’s account to a merchant’s account when an electronic transaction is initiated. Although the process completes in under two seconds from the consumer’s perspective, it involves a structured chain of communications between multiple regulated entities — including the merchant, the payment processor, the acquiring bank, the card network, and the issuing bank — each performing a distinct function within the transaction lifecycle.
The global payment processing market was valued at approximately $71.5 billion in 2026 and is projected to reach $122 billion by 2031, according to industry estimates. That growth trajectory reflects both the continued migration of commerce from cash to electronic payment methods and the expanding complexity of the payment stack, as businesses increasingly operate across multiple channels, geographies, and currencies simultaneously.
Understanding how payment processing infrastructure functions has direct relevance for businesses selecting a payment stack, for financial institutions evaluating integration requirements, and for policymakers assessing the competitive and regulatory implications of an industry undergoing structural change. The emergence of account-to-account payments, real-time settlement networks, and stablecoin-based cross-border transactions is challenging the card network rails that have defined payment processing for decades.
The Five Parties in a Card Transaction
Every standard card payment involves five distinct parties, each occupying a defined role in the authorisation and settlement chain.
The cardholder initiates the transaction by presenting payment credentials — physically via a point-of-sale terminal or digitally via an e-commerce interface. The issuing bank is the financial institution that issued the card and holds the cardholder’s account; it is responsible for approving or declining the authorisation request. The card network — operated by companies including Visa, Mastercard, and American Express — establishes the rules governing transaction processing and routes authorisation messages between the issuing and acquiring banks. The acquiring bank holds the merchant’s account and receives settlement funds on the merchant’s behalf. The payment processor is the technology and operational layer that sits between the merchant and the acquiring bank, transmitting authorisation requests, applying fraud rules, and managing settlement data.
The boundaries between these roles are not always distinct. American Express operates as both issuing bank and card network for its proprietary products. Payment facilitators such as Stripe, Braintree, and PayPal bundle gateway, processing, and acquiring functions under a single contractual relationship. Some processors also act as acquirers, offering end-to-end solutions that reduce the number of counterparties a merchant must manage directly.
How Payment Processing Works: Authorisation, Capture, and Settlement
A card payment moves through three sequential stages: authorisation, capture, and settlement. Each stage involves distinct operations and different parties.
Authorisation
When a customer initiates a transaction, the merchant’s payment gateway captures the card credentials and encrypts the data before transmitting it to the payment processor. Encryption and tokenisation at this stage ensure that raw card data is not transmitted in a form that could be intercepted and misused. The processor forwards the transaction details to the card network, which routes the authorisation request to the issuing bank.
The issuing bank reviews the request against the cardholder’s available balance or credit limit, performs identity and fraud checks, and returns either an authorisation code or a decline message through the same chain — card network to processor to merchant — typically within milliseconds. If approved, the merchant may proceed with the transaction; if declined, the merchant must request an alternative payment method.
Capture
Authorisation reserves the funds but does not transfer them. Capture is the instruction from the merchant to the processor to collect the authorised amount. For in-store transactions, capture typically occurs in a batch process at end of day. For e-commerce transactions, capture is often immediate upon order confirmation, though some merchants delay capture until goods are dispatched.
Settlement
Settlement is the process by which funds are physically transferred between banking institutions. The processor submits the captured transaction batch to the acquiring bank, which initiates the interbank transfer via the card network. The merchant’s account is credited with the transaction amount, net of applicable fees, typically within one to three business days of the transaction date.
Fee Structures: Interchange, Scheme Fees, and Acquirer Margins
Merchant transaction fees are composed of three distinct layers, which may be presented separately or bundled into a single merchant service charge depending on the pricing model applied.
Interchange fees are paid by the acquiring bank to the issuing bank for each transaction processed. They are set by the card network and typically range from 0.5% to 2% of the transaction value, varying by card type, merchant category, and geography. Interchange fees represent the largest component of the total merchant service charge and compensate the issuing bank for the cost and risk of extending credit or debit services to the cardholder.
Scheme fees are paid to the card network operator — Visa, Mastercard, or an equivalent — for the use of its routing and rules infrastructure. These fees are generally smaller in absolute terms than interchange fees but have increased as a proportion of the total fee stack in recent years.
The acquirer margin represents the processing company’s revenue for the services it provides, including gateway connectivity, fraud management, and settlement operations.
These three components are commonly bundled into a single rate under flat-rate pricing models — Stripe’s standard rate of 2.9% plus $0.30 per transaction is a widely cited example. Interchange-plus pricing presents each component separately, allowing higher-volume merchants to optimise costs by negotiating on the acquirer margin while the interchange and scheme fee components remain fixed by the card network.
Payment Gateways, Payment Facilitators, and Merchant Account Structures
A payment gateway is the software interface that connects a merchant’s point-of-sale system or e-commerce platform to the acquiring bank’s processing infrastructure. It handles data capture, encryption, and the transmission of authorisation requests and responses.
Payment facilitators — also referred to as payfacs — combine gateway, processing, and acquiring functions under a single contract, placing merchants on a shared merchant account rather than requiring each merchant to establish a direct relationship with an acquiring bank. This model significantly reduces the complexity and time required for merchant onboarding. Stripe, PayPal, and Square operate under this model. The trade-off is that merchants on shared accounts are subject to greater risk of account holds or terminations, as the facilitator manages aggregate risk across its entire merchant portfolio.
Traditional acquiring — in which a merchant maintains a dedicated merchant account with an acquiring bank — remains the standard for higher-volume businesses, where the operational complexity is justified by greater control over account stability and fee negotiation.
Payment Card Industry Data Security Standard compliance, universally referred to as PCI DSS, applies to all entities that store, transmit, or process cardholder data. Processors and facilitators are required to maintain PCI DSS certification and integrate compliance requirements into their platforms, reducing but not eliminating the compliance burden on merchants.
Alternative Payment Rails: A2A Payments, Real-Time Networks, and Stablecoin Transactions
Card networks represent the dominant infrastructure for retail payment processing, but they are facing structural competition from alternative payment mechanisms that bypass card rails entirely or operate on different settlement architectures.
Account-to-Account Payments
Account-to-account payments, enabled by open banking API frameworks such as the EU’s Payment Services Directive 2 and the UK Open Banking Standard, allow payment initiation directly from a consumer’s bank account without routing through a card network. Transaction costs for A2A payments are materially lower than card-based alternatives — card payments typically cost merchants 1.5% to 3% of transaction value, while A2A payments are processed at significantly lower per-transaction rates. Industry participants including GoCardless have indicated that A2A payments are positioned to become a primary alternative to card rails, contingent on broader infrastructure development and consumer adoption.
Real-Time Payment Networks
National and regional real-time payment infrastructures — including the UK’s Faster Payments Service, the EU’s SEPA Instant Credit Transfer, India’s Unified Payments Interface, and the US Federal Reserve’s FedNow service — enable settlement in seconds on a 24-hour, seven-day basis, compared with the one-to-three business day settlement cycle of card-based transactions. These networks are increasingly relevant for both consumer and business payment scenarios where settlement speed carries commercial value.
Variable Recurring Payments
Variable Recurring Payments, enabled under the UK Open Banking Standard, allow authorised third parties to initiate recurring payments of variable amounts from a consumer’s bank account within pre-agreed parameters. VRPs represent a technically more flexible alternative to traditional direct debit mandates and are subject to ongoing commercial pilot programmes in the UK market.
Stablecoin Payments
Stablecoin-denominated transactions are emerging as an alternative mechanism for cross-border business-to-business payments, where the cost and settlement delay of traditional wire transfers represent a material operational friction. While stablecoin payment infrastructure for retail use cases remains at an early stage of development, the business-to-business cross-border segment has attracted growing institutional interest from financial institutions and technology providers seeking alternatives to correspondent banking rails.
Risks, Fraud Management, and Security Infrastructure
Fraud management is an integral function of payment processing infrastructure. Payment processors apply rule-based and machine-learning fraud detection systems at multiple points in the transaction flow, analysing transaction characteristics in real time against established behavioural baselines and known fraud patterns.
Chargebacks — disputes initiated by cardholders that result in the reversal of a transaction — represent a related risk category with direct cost implications for merchants. The chargeback process is governed by card network rules and involves the issuing bank, acquiring bank, and processor. Industries with elevated chargeback exposure, including travel, telecommunications, and certain regulated categories, may face processor restrictions or require specialist acquiring relationships.
Tokenisation replaces sensitive card data with a unique identifier, or token, that has no exploitable value outside the specific transaction context for which it was generated. This approach limits the exposure of cardholder data across the payment chain and reduces the scope of PCI DSS compliance requirements for merchants.
Strong Customer Authentication requirements, mandated under PSD2 for transactions in the European Economic Area, require additional verification steps — such as biometric confirmation or a one-time passcode — for electronic payments above specified thresholds, adding a layer of fraud protection at the point of transaction initiation.
Conclusion
Payment processing infrastructure connects merchants, financial institutions, and card networks through a structured sequence of authorisation, capture, and settlement operations that have underpinned electronic commerce for several decades. The fee structures embedded in this infrastructure — interchange, scheme fees, and acquirer margins — reflect the cost and risk allocation between parties, and have been subject to increasing regulatory scrutiny in multiple jurisdictions.
The emergence of account-to-account payment rails, real-time settlement networks, and alternative cross-border mechanisms represents a structural challenge to the card network model. Whether these alternatives achieve the scale necessary to displace card-based processing as the dominant retail payment mechanism depends on infrastructure development, regulatory support, and consumer adoption trajectories that remain open variables. For businesses and financial institutions, understanding the architecture of the payment processing chain is a prerequisite for evaluating these developments and their commercial implications.
