docs(x402): fix gasless upto setup and v2 header names (verified e2e)#14
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Found via real end-to-end runs against the public Sepolia facilitator (0-ETH buyer paying gasless `upto`): - Seller quickstart omitted `declareEip2612GasSponsoringExtension()` on the `upto` route. Without it the facilitator can't sponsor the buyer's Permit2 approval, so a 0-ETH buyer is rejected with `permit2_allowance_required` once its standing allowance is exhausted. Add the extension + explanation, and add `@x402/extensions` to install/package list. - Header names were the x402 v1 spelling. This (v2) SDK uses `payment-response` (receipt), `payment-signature` (request), `payment-required` (402). Fix the buyer receipt code, the how-it-works diagram/text, and prose across pages. - Soften the `receipt.amount` note (it is optional in SettleResponse).
Verified e2e against the public Sepolia facilitator with a 0-ETH buyer: both `exact` and `upto` settle on-chain while the buyer's ETH stays 0 — the facilitator submits settlement and pays the gas. The previous wording claimed `exact` needs buyer ETH and only `upto` could be gasless; that is backwards. Correct the Buyers prerequisites/intro and the Networks & Token funding section: the buyer needs no ETH for `exact`, and none for `upto` when the seller enables EIP-2612 sponsoring (only a non-sponsored upto's one-time Permit2 approval costs the buyer a little ETH).
…ippet - how-it-works: state that the facilitator relays settlement and pays gas for `exact` (buyer needs no ETH), and that `upto`'s only extra cost is the one-time Permit2 approval, sponsored when the seller enables it. Keeps the scheme overview consistent with the Buyers/Networks guidance. - sellers: note the "Accepting upto" snippet replaces the step-4 route and reuses the same `price` / `PAY_TO`.
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Follow-up to #13. These fixes were found by running the documented Quickstart: Sellers and Quickstart: Buyers code verbatim against the public HPP Sepolia facilitator (a 0-ETH buyer paying gasless
upto).Bug 1 — Seller quickstart omitted the gasless extension
The
uptoroute did not declaredeclareEip2612GasSponsoringExtension(). Without it the facilitator can't sponsor the buyer's Permit2 approval, so a 0-ETH buyer is rejected withpermit2_allowance_requiredonce its standing allowance is exhausted (reproduced: allowance9951 < 10000→ 412; after adding the extension → settles).uptoand gasless payments"@x402/extensionsto install line and the SDK package table:::noteon the Facilitator pageBug 2 — v1 header names
The docs used the x402 v1 header spelling. This (v2) SDK uses:
payment-signature(docs saidX-PAYMENT)payment-response(docs saidX-PAYMENT-RESPONSE)payment-requiredThe buyer's receipt code read
x-payment-response, so it never fired. Fixed the buyer code, the how-it-works diagram/text, and prose across pages. Also softened thereceipt.amountnote (it is optional inSettleResponse).Verification
After the fixes, the documented buyer code returns
200and prints the receipt:SETTLED tx: 0xb8cdc6f3…34f4 network: eip155:181228, with the buyer's USDC.e balance decreasing on-chain — all gasless (buyer holds 0 ETH).npm run buildpasses with `onBrokenLinks: 'throw'`.