Agentic commerce introduces a new trap: a signature that makes a checkout feel frictionless can leave token spending authority behind. This engineering guide examines ERC-2612 permits as payment permissions rather than as completed payments, with checks that product teams can test before an AI agent moves money.

Why a signed permit is not a payment instruction

An AI agent that purchases an API call or pays a creator might request permission to spend ERC-20 tokens. An ordinary approve transaction sets an allowance on-chain, while a subsequent transferFrom can use that allowance. ERC-2612 adds permit, which lets a token owner sign an EIP-712 typed message authorizing an allowance update without first broadcasting an approval transaction. That can simplify onboarding, but it also creates a dangerous user-experience shortcut: people may mistake a wallet signature for a harmless login. The ERC-2612 specification, originally created April 13, 2020, defines allowance authorization, not a purchase receipt, price guarantee, or completed transfer. An agent should therefore separate the language of permission from the language of payment. If a checkout screen says “pay $5 now” but collects permission to spend $500 later, its authorization model is broken even if the underlying signature verifies.

Five fields that must be visible before signing

A permit includes the token domain, owner, spender, value, nonce and deadline. The EIP-712 domain binds the signature to context such as the chain and verifying contract; the nonce helps prevent successful replay; the deadline limits when the signed authorization can be submitted. A responsible agent interface should make these details inspectable in plain language. Show the token contract and chain, the intended counterparty’s spender address, the exact maximum token amount, and the last time the permit may be exercised. Present the amount in human-readable units using the correct token decimals, but retain raw units in transaction logs. Avoid hiding a third-party payment router behind a vague “service provider” label. When an agent uses many tools, attach a local transaction-intent ID to the permit request, so a later incident report can trace which user instruction led to this specific approval. None of these displays substitutes for signature verification, but together they make a meaningful informed choice possible.

Deadline does not mean the allowance expires

This is the most consequential distinction for product teams. The deadline in ERC-2612 limits the time during which the permit signature may be submitted. Once a successful permit sets an allowance, the allowance does not automatically disappear when that original signing deadline passes. The token’s allowance rules determine what happens next. OpenZeppelin’s ERC20Permit documentation explicitly describes a signed approval that updates a spender allowance, and its ERC-20 implementation notes the continuing risks of ordinary approvals. A product saying “this authorization expires in ten minutes” may therefore mislead users if it means only the signature submission window. Use two distinct labels: “signature valid until” and “spending permission currently remaining.” When practical, authorize the smallest amount needed for a single purchase and verify or clear residual approval after settlement, recognizing that clearing an on-chain allowance can itself require another transaction.

Build a transaction-scoped payment envelope

An AI payment controller should enforce independent checks beyond the ERC-2612 signature. For each agent action, create a policy envelope with the approved merchant, token, amount ceiling, purpose, expiry for the business instruction, and a human confirmation state. Before spending, validate the contract addresses against an allowlist, confirm the user-approved price and item, re-check the chain ID, and reserve budget to prevent two concurrent tasks from spending against the same ceiling. This business envelope is an application-level control; it is not guaranteed by ERC-2612 itself. For recurring subscriptions, document the recurring limit and termination process separately from one-off permits. In an illustrative $20 research-credit purchase, an approval of exactly $20 equivalent is preferable to an unlimited allowance where supported, because the potential future exposure is smaller. But an exact amount can still be abused by the wrong spender, so address verification remains essential.

Handle races, smart wallets and failed relayers

The ERC-2612 rationale notes that a relayer may submit or withhold a signed permit, and that another party can submit the same valid signature first. OpenZeppelin illustrates a tolerant integration pattern: attempt permit and then use a standard transfer path, while not assuming that the permit call must succeed in the same transaction. Such behavior needs careful replay-safe business logic. A successful permit update is not evidence that the merchant received funds. Confirm the actual transfer event and settlement state before fulfilling a paid entitlement. Moreover, standard ERC-2612 signatures are generally oriented around externally owned account signing; smart contract wallets may require different signature interfaces or a fallback transaction. The agent should never silently switch to a broader authorization scheme to “make the payment work.” It should stop, explain the change, and ask the user to approve the revised action.

What to test before enabling real money

Test the authorization flow against deliberate faults: expired permit, reused nonce, wrong token address, wrong chain, malicious spender, precision mismatch, allowance remaining after expiry, concurrent checkout, reverted transfer and compromised relayer. Capture the displayed user instruction, typed-data payload hash, chain and contract identifiers, on-chain transaction hashes and the final balance change. Protect this audit record from unnecessary exposure of personal chats. Evaluate not just successful payments, but also whether a user can cancel before signing and recover after a partial failure. For AI agents, the engineering principle is simple: authentication proves who requested an action, an allowance limits who may move assets, and settlement proves what actually happened. None is interchangeable with the others. A secure payment workflow keeps these boundaries visible even when an AI assistant tries to collapse every step into one convenient button.

Sources and further reading

Primary specifications consulted October 24, 2026: Ethereum Improvement Proposal 2612, created April 13, 2020; OpenZeppelin Contracts 5.x ERC20Permit documentation (current reference, accessed October 24, 2026).

Cover photo: Markus Spiske / Unsplash.