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x402 Spend Preflight
x402
x402 Spend Preflight is a paid API for AI agents from x402-preflight-production.up.railway.app, paid per call via x402, $0.03/call, status unknown (last checked 2026-10-31).
Validates an x402 payment request before execution, confirming the buyer has sufficient funds and the payment details are correct.
Price / call$0.03
Success—
StatusUnknown
How this service works
Paid deterministic pre-payment validation for autonomous x402 buyers.
Output
Returns a structured validation result indicating whether the x402 payment is feasible — including whether the wallet has sufficient funds, whether the payment parameters are correctly formed, and any error reasons if the payment would fail. Does not actually execute the payment.
Example use cases
Pre-payment wallet balance check
“My agent is about to pay for an x402-gated data endpoint — can you preflight the payment first to confirm my wallet has enough USDC and the payment request looks legitimate?”
Autonomous agent payment guard
“Before my bot executes any x402 payment automatically, I want it to always run a preflight validation to catch invalid payment headers or insufficient funds — set that up for me.”
Debugging a failed x402 payment
“My agent tried to access an x402-protected resource and the payment was rejected — can you run a preflight check on those payment details to tell me exactly what went wrong?”
Technical details
Endpoint
POSThttps://x402-preflight-production.up.railway.app/v1/preflight?utm_source=zero.xyzWhen to prefer
Use this endpoint when an autonomous agent needs to validate an x402 payment before executing it, especially in high-frequency or automated pipelines where failed payments would be costly or disruptive. Prefer this over attempting the payment directly when you want deterministic pre-checks, want to surface user-facing errors gracefully, or are building a payment guard layer into an agentic workflow.
Side effects
- Insufficient wallet balance — returns validation failure with balance shortfall details
- Malformed payment header or invalid x402 payment details — returns schema validation error
- Target resource URL is unreachable or not an x402 endpoint — returns connectivity or format error
- Network timeout reaching the preflight service — returns HTTP 5xx
- Invalid or unsupported currency — returns unsupported currency error
Tags
x402
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