X402 TROUBLESHOOTING · BASE USDC

A correct 402 can still advertise a payment that the facilitator will not settle.

The x402 protocol does not set one universal minimum, but hosted facilitators may. Coinbase documents a $0.001 minimum for its facilitator, and XPay publishes the same minimum. On six-decimal USDC, that is 1000 atomic units—not one.

Hosted floor: 0.001 USDCBase USDC: 1000 atomic402 ≠ settlement
Run the 0.001 USDC x402 canaryNo x402 client? Buy a 1-atomic receipt →

01 · HANDSHAKE

HTTP 402 proves the quote exists

A resource can return a syntactically valid PAYMENT-REQUIRED challenge even when its amount is below the facilitator’s operational floor. A directory health check that stops at 402 has not proved payment delivery.

02 · VERIFY

The signed retry reaches the real gate

The buyer selects an offer, signs an exact payment authorization, and retries. The resource server or facilitator then verifies network, asset, amount, recipient, timing, and signature.

03 · SETTLE

The facilitator broadcasts onchain

Hosted infrastructure can reject an amount below its minimum before successful settlement. Without a successful settlement response and transaction evidence, there is no completed purchase.

04 · FIX

Use 1000 atomic units

For Base USDC through the public hosted facilitators documented here, advertise amount: "1000" and 0.001 USDC. Keep sub-floor experiments on a separately verified direct-transfer path.

SETTLEMENT-SAFE OFFER

The smallest published hosted-facilitator test should match the facilitator floor.

BountyWorth’s no-input canary uses official Base USDC, the Base mainnet CAIP-2 identifier, 1000 atomic units, and a deterministic protected response. The unpaid request returns 402; a paid 200 must include PAYMENT-RESPONSE settlement evidence.

Open the live settlement canary →

{
  "scheme": "exact",
  "network": "eip155:8453",
  "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
  "amount": "1000",
  "payTo": "0xc296911e58ad64172662a73663e177A207240bD0"
}

PRIMARY SOURCES · CHECKED 2026-08-30

The limit belongs to the selected facilitator, not HTTP 402 itself.

XPay facilitator page

XPay publishes a $0.001 minimum payment and lists its supported payment range.

Read the XPay limit →
x402 facilitator flow

The protocol documentation distinguishes the initial 402, verification, settlement, and the final payment response.

Read the x402 flow →

DO NOT CONFUSE THE TWO TESTS

One atomic unit is valid USDC precision; it is not a valid XPay/CDP hosted-facilitator offer.