How Payment Systems Work

Domestic Payment Rails

In the United States, most business-to-business payments move across one of three networks: ACH, Fedwire, or CHIPS. Each has a different cost structure, settlement timeline, and appropriate use case.

ACH (Automated Clearing House)

ACH is a batch network operated by Nacha (formerly NACHA). It processes over $80 trillion in payments annually. Transactions are collected throughout the day, batched, and sent to the clearing system multiple times per day.

Standard ACH settles in 1-3 business days. Same Day ACH, launched in 2016 and expanded to credits in 2017, settles same-day if submitted before the 2:30 PM ET cut-off - but the per-transaction cap was raised to $1 million per payment in 2022, making it viable for most business payments.

Per-transaction cost: $0.20-$1.50, though most payment processors charge a percentage on top. ACH returns (failed payments) add operational overhead - the return window can be up to 60 days for unauthorized transactions, which is a meaningful chargeback exposure for recurring billing businesses.

Fedwire

Fedwire Funds Service is operated by the Federal Reserve and provides real-time gross settlement (RTGS) - each payment settles individually, immediately and irrevocably. Banks must hold Federal Reserve accounts to participate directly.

Settlement is final within seconds of processing. The Fed charges $0.83 per transaction (as of 2024) to sending and receiving institutions combined. But your bank may charge $15-$50 on top as a wire fee passed to the customer.

Fedwire handles about $4.5 trillion per day. It operates Monday through Friday 9 AM - 7 PM ET. This operating window is a recurring constraint that becomes visible the moment you try to settle with counterparties in different time zones.

CHIPS

CHIPS (Clearing House Interbank Payments System) is operated by The Clearing House, a consortium of large banks. It handles $1.5 trillion per day in large-value, primarily cross-border US dollar transactions.

Unlike Fedwire's gross settlement, CHIPS uses multilateral netting - it queues payments throughout the day and offsets debits against credits between participants. This reduces the amount of liquidity that needs to move between accounts. CHIPS settles its net positions through Fedwire at day's end. The netting efficiency typically means that $1.5 trillion of daily payment flows settles with only ~$30B in actual funds movement.

Card Networks and Interchange

When a customer pays with a Visa or Mastercard, the money does not flow directly from the customer's bank to yours. It passes through four parties, each taking a cut.

Interchange is the fee the acquirer pays to the issuer on every transaction. It is set by the card networks (Visa, Mastercard) and varies by card type, merchant category code (MCC), and transaction method:

• Consumer debit cards (Durbin-regulated, banks >$10B assets): capped at $0.21 + 0.05%
• Consumer credit cards: typically 1.5%-2.0% for basic cards
• Premium rewards / travel cards: 2.5%-3.5% - the merchant pays for your airline miles
• Corporate purchasing cards: 2.5%-3.5%, card-not-present adds additional basis points

PCI-DSS compliance is a mandatory cost layer on top of interchange. Any entity that stores, processes, or transmits cardholder data must comply with the 12 PCI requirements. The cost ranges from a few hundred dollars per year for a small merchant using a compliant third-party processor (who takes on most of the PCI scope) to $200K+ annually for a large merchant running their own payment systems.

Chargebacks add a final layer of cost: typically $20-$100 per dispute in fees, plus the lost revenue if the dispute is ruled in the customer's favor. High chargeback rates (above 1% of transactions) can trigger reserve requirements or account termination by the acquirer.

SWIFT and Correspondent Banking

SWIFT is a secure messaging network, not a settlement system. When your bank sends a SWIFT message, it is instructing another bank to credit or debit an account. The actual money moves through pre-established correspondent banking relationships.

How correspondent banking works

Consider a US company paying a supplier in Vietnam. The US company's bank almost certainly does not have a direct relationship with a Vietnamese bank. So the payment routes through intermediaries:

Nostro and vostro accounts

To facilitate cross-border payments, banks maintain pre-funded accounts at correspondent banks abroad. When Bank A holds an account at Bank B in Bank B's local currency, Bank A calls it a nostro account ("ours"). Bank B calls the same account a vostro account ("yours").

This pre-funding model requires capital to sit idle across potentially hundreds of correspondent relationships globally. Industry estimates put the total trapped liquidity in nostro/vostro accounts at $25-$27 trillion globally. That tied-up capital earns nothing, drives correspondent banking fees, and is the primary inefficiency that on-chain settlement aims to replace.

The World Bank's Remittance Prices Worldwide database consistently shows average cross-border retail transfer costs of 6%+ globally, with some corridors in Sub-Saharan Africa exceeding 10%. Business-to-business corridors fare better (1.5%-3% for USD-EUR), but the fundamental structural costs remain.

SWIFT GPI

SWIFT launched GPI (Global Payments Innovation) in 2017 to address speed and tracking. GPI payments come with an end-to-end tracking reference, a credit confirmation when funds arrive, and a commitment (not always met) to same-day settlement within business hours. As of 2024, over 50% of SWIFT payment messages are GPI, and 90%+ of GPI payments credit within 24 hours. This is a meaningful improvement over pre-GPI norms, but still operates within the constraints of the correspondent banking network.

ISO 20022 and the SWIFT Migration

ISO 20022 is the global standard for financial messaging that is now replacing the legacy SWIFT MT format family. This migration matters for anyone evaluating blockchain payment infrastructure because ISO 20022 is the interoperability layer that will connect legacy banking systems to blockchain rails for the foreseeable future.

The MT format problem

SWIFT MT messages (MT103, MT202, MT900 series) are flat-file formats dating to the 1970s. They have fixed field structures, limited field lengths, and no standardized way to carry remittance data. An MT103 for a USD wire has 72 bytes for remittance information. Free-text fields lead to inconsistent formatting across institutions - a payment reason that one bank writes as "Invoice #12345" another writes as "INV-12345" or "12345 Apr". Systems cannot reliably parse this machine-to-machine, so humans intervene to repair messages, adding cost and delay.

What ISO 20022 changes

ISO 20022 uses XML-based MX message formats with a formal data dictionary. Key improvements:

• 10x more structured data fields compared to MT equivalents
• Remittance data travels with the payment (structured invoice references, line-item detail)
• Machine-readable fields enable straight-through processing (STP)
• Standardized Legal Entity Identifiers (LEI) and BIC codes in required fields
• Richer AML/KYC data embedded in the message, reducing manual compliance checks

Migration timeline and current status

SWIFT's cross-border payment migration to ISO 20022 MX formats was originally scheduled to complete in November 2025. The coexistence period (during which both MT and MX messages were accepted) ran from March 2023 through November 2025. As of late 2025, institutions that have not migrated face rejection of non-compliant MT messages on SWIFT's cross-border network.

Domestically, major markets have their own timelines. The Fed's FedNow service launched in July 2023 and uses ISO 20022 natively. The UK's CHAPS migrated in 2023. The Eurozone's TARGET2 migrated in November 2022. The US ACH network (Nacha) has ISO 20022 mapping rules but the full migration of domestic ACH to ISO 20022 is ongoing.

Cross-Border Pain Points: The Numbers

Before evaluating blockchain alternatives, it helps to quantify what the current system actually costs your business.

Beyond fees, there are operational costs that don't show up in the transaction fee line:

• Treasury management: capital tied up in float during settlement windows
• FX risk: exchange rates can move 0.5%-3% during a multi-day settlement
• Compliance overhead: sanctions screening, KYB on counterparties, AML checks
• Reconciliation: matching payments to invoices when remittance data is garbled
• Failed payment recovery: tracking down where in the correspondent chain a payment stopped

These are the actual pain points blockchain payment networks are being built to address. Not every business faces all of them. A domestic-only, card-accepting retail business has a different problem set than an importer paying Asian suppliers weekly. Module 6 will help you identify which pain points apply to your situation and which payment alternatives are actually worth evaluating.

What This Means for Your Evaluation

Every blockchain payment solution is ultimately selling against one or more of these failure modes in the legacy system. The value proposition only holds if the failure mode it solves is one your business actually experiences at a cost that exceeds the switching cost.

Lightning Network makes sense if you have high-frequency small payments and need near-zero fees with instant settlement. USDC on Solana makes sense if you're doing cross-border B2B payments and the FX conversion and correspondent bank fees are significant relative to your margins. BTCPay Server makes sense if you want self-custody of crypto revenue without paying 1%-2% to a payment processor.

None of these make sense universally. The rest of this course gives you the technical and regulatory knowledge to evaluate each option against your specific situation. Module 2 covers the blockchain payment stack in detail. Come back to this module's framework when you're evaluating a specific tool - the question is always: which legacy pain point does this solve, and does the cost reduction justify the operational complexity of adding a new payment rail?