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x402 Payment Preflight
x402
x402 Payment Preflight is a paid API for AI agents from api.delx.ai, paid per call via x402, $0.002/call, status unknown (last checked 2026-10-19).
Validates x402 HTTP 402 payment requirements against caller-defined constraints (max USDC amount, allowed networks, scheme, recipient, expiry) before a wallet signs, returning eligible accepts and any blockers.
Price / call$0.002
Success—
StatusUnknown
How this service works
Evaluate caller-supplied x402 payment requirements before a wallet signs them. Use after receiving HTTP 402 to enforce a maximum USDC amount, allowed networks, exact scheme, recipient presence, and an optional expiry buffer. Returns eligible accepts and explicit blockers for 0.002 USDC via x402 on Base; it never signs, pays, stores, or echoes a payment signature.
Output
Returns a list of eligible payment accepts that pass all caller-supplied constraints, plus an explicit list of blockers (e.g. amount too high, disallowed network, missing recipient, insufficient expiry) explaining why any accepts were rejected. Never signs, pays, stores, or transmits a payment.
Example use cases
Enforce USDC spending cap on 402 payment
“I just got an HTTP 402 response with these payment requirements — can you check whether the requested amount is under 0.01 USDC and only on Base before my agent's wallet commits to anything?”
Block unsupported network payment
“My agent received an x402 payment challenge and I want to make sure it's restricted to Base or Ethereum mainnet only — run a preflight and tell me if there are any blockers or if it's safe to proceed.”
Expiry buffer safety check before signing
“Before signing this x402 payment, verify that the payment window won't expire in the next 2 minutes — I need at least 120 seconds of buffer to avoid a race condition.”
Technical details
Endpoint
POSThttps://api.delx.ai/api/v1/x402/payment-preflight?utm_source=zero.xyzWhen to prefer
Use this endpoint immediately after receiving an HTTP 402 response when your agent needs to enforce a spending policy, network allowlist, or expiry safety buffer before authorizing a wallet signature. Prefer it over ad-hoc client-side checks when you want a structured, auditable list of blockers and eligible accepts rather than rolling your own x402 validation logic.
Side effects
- Missing or malformed requirements object returns a validation error
- max_amount_usdc set to 0 blocks all accepts
- allowed_networks list contains network identifiers not present in the payment requirements, resulting in all accepts blocked
- now_epoch_seconds not provided may cause incorrect expiry evaluation
- Payment requirements with no recipient field may trigger a blocker if recipient presence is enforced
- Service returns HTTP 402 itself (costs 0.002 USDC per call via x402)
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| requirements | object | |
| asset_decimals | integer | |
| max_amount_usdc | number | |
| allowed_networks | array | |
| now_epoch_seconds | integer | |
| min_expiry_seconds | integer |
Output
Schema · Response
{
"type": "json",
"example": {
"policy": {
"asset_decimals": 6,
"expiry_checked": true,
"max_amount_usdc": "0.002",
"allowed_networks": [
"eip155:8453"
],
"min_expiry_seconds": 30
},
"schema": "delx/util-x402-payment-preflight/v1",
"approved": true,
"selected": {
"index": 0,
"pay_to": "0x1111111111111111111111111111111111111111",
"scheme": "exact",
"network": "eip155:8453",
"amount_usdc": "0.001",
"expiry_status": "ok"
},
"evaluations": [
{
"index": 0,
"scheme": "exact",
"network": "eip155:8453",
"blockers": [],
"amount_usdc": "0.001",
"expiry_status": "ok",
"pay_to_present": true
}
],
"eligible_count": 1,
"evaluated_count": 1
}
}Tags
x402
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