Stablecoin Payments 101

What a payment stablecoin actually is

A payment stablecoin is a token on a public blockchain that is redeemable 1:1 for a fiat currency, backed by a segregated reserve of cash and short-dated government debt, with regular third-party attestations that the reserve covers the float. Technically it is just a token contract — an ERC-20 on Ethereum-family chains, an SPL token on Solana, an issued currency on XRPL — and moving it is a single contract call:

• Transfer — transfer(to, amount), where amount is an integer in the coin's on-chain decimals (USDC uses 6, not 18 — decode a real one in the Calldata Decoder).
• Authorized transfer — EIP-3009 lets a holder sign a transfer off-chain that anyone can submit; this is the primitive x402 machine payments are built on.
• Issuer controls — regulated issuers retain mint, burn, freeze and blocklist powers; sanctioned addresses can and do get frozen. This is a feature for regulators and a design constraint for engineers.

The regulatory frame

Two regimes define the coins the card networks are willing to settle in:

• GENIUS Act (US) — the federal payment-stablecoin law: licensed issuers, 1:1 high-quality liquid reserves, redemption rights, and supervision. The coins in the settlement programmes below are GENIUS-aligned or NYDFS-chartered (Paxos-issued PYUSD, USDG, USDP).
• MiCA (EU) — stablecoins are "e-money tokens"; issuance in the EU requires an EMI/credit-institution licence. Circle's USDC and EURC are MiCA-compliant, which is why they dominate EU-facing use.

USDT (Tether) remains the largest stablecoin by float but sits outside both frames — offshore issuance, no card-network settlement programme. It matters for volume, not for regulated payments infrastructure.

The card-network settlement shift

The structural change is easy to misread: consumers are not paying with stablecoins at the point of sale. Authorization stays exactly as it is — ISO 8583 messages, EMV cryptograms, network tokens. What moves on-chain is settlement: the money movement between acquirers, networks and issuers after clearing.

• Visa has settled in USDC since its 2023 pilot, expanded to USDC, EURC, PYUSD and USDG across Ethereum, Solana, Stellar and Avalanche (July 2025), and launched US-domestic USDC settlement over Solana in December 2025.
• Mastercard expanded settlement in June 2026 to USDC, RLUSD, PYUSD, USDG, USDP and SoFiUSD across Arbitrum, Base, Canton, Ethereum, Polygon, Solana, Tempo and XRPL — and closed its up-to-$1.8B acquisition of BVNK on August 3, 2026, becoming the first network to own stablecoin settlement infrastructure.
• Open USD (OUSD) — the consortium coin announced June–July 2026, designed as shared settlement infrastructure rather than a single-issuer product.

For engineers this means reconciliation gains on-chain fields — chain, contract, tx hash, finality timestamp — that have no ISO 8583 equivalent, while disputes and reversals have no on-chain equivalent. The two worlds meet in your recon layer.

The coin landscape

The regulated, payment-relevant set — the coins Visa and Mastercard accept or plan to accept for settlement, plus USDT for completeness. Click through for per-coin detail: chains, contract addresses, reserves, and dated sources.

Full reference with contract addresses per chain, reserve models and regulation detail: Stablecoin Reference.

Where stablecoins show up in payments

• Network settlement — acquirer/issuer settlement in USDC & co., as above. Invisible to cardholders.
• Pay-ins and payouts — platforms accepting stablecoin deposits and paying out to wallets, with a provider handling quotes, conversion, monitoring and gas. This is BVNK's model — step through it below.
• Cross-border B2B — treasury moves that would otherwise ride correspondent banking; the same problem SWIFT's shared ledger attacks with tokenised deposits instead of stablecoins.
• Machine payments — x402 uses signed EIP-3009 stablecoin authorizations as the payment instrument for APIs and AI agents; the agentic stack (AP2's crypto extension) settles the same way.

The interactive below shows a stablecoin pay-in end to end — quote lock, unique deposit address, on-chain detection, confirmation and signed webhook:

Finality changes the failure model

Card rails assume reversibility: authorization can be voided, clearing adjusted, transactions charged back for 120+ days. On-chain transfers are the opposite — final in seconds, unrecallable by design. Practical consequences:

• No chargebacks — refunds become application-level: a new transfer in the opposite direction, initiated by the payee.
• Address validation is the last line of defence — funds sent to a wrong or wrong-network address are gone. Validate before broadcast (Wallet Address Validator); hosted deposit pages exist largely to eliminate mistyped addresses.
• Underpayment and expiry are first-class states — quote-locked pay-ins end COMPLETE, UNDERPAID or EXPIRED, and those states are immutable; your integration has to handle all three.

Related reading & tools

Stablecoin Reference · Calldata Decoder · Wallet Address Validator · BVNK Flow Simulator · x402 Flow Simulator