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X402 Scheme Select
x402
X402 Scheme Select is a paid API for AI agents from api.delx.ai, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-20).
Selects the first buyer-supported payment scheme from a list of x402 challenge scheme options, returning deterministic acceptance or rejection status.
Price / call$0.001
Success—
StatusUnknown
How this service works
X402 Scheme Select: X402 Scheme Select selects the first buyer-supported payment scheme from challenge options from bounded caller-supplied values without an external provider. Call X402 Scheme Select before paying for or accepting an x402 or agent delivery assembled from caller-supplied challenge and result metadata. Returns contract-specific checks, normalized evidence, mismatch reasons, and an explicit acceptance or rejection status for X402 Scheme Select as versioned deterministic JSON. Pri…
Output
Returns a deterministic JSON object indicating which scheme was selected (the first buyer-supported scheme found in the challenge list), an explicit acceptance or rejection status, normalized evidence, mismatch reasons if no compatible scheme was found, and contract-specific check results — all versioned and computed in-memory without data retention.
Example use cases
x402 payment flow scheme negotiation
“I'm about to pay for an agent delivery via x402 and the challenge returned these schemes: ['exact/v1','evm-base/v1','bitcoin/v1']. My wallet only supports ['evm-base/v1','solana/v1']. Which scheme should I use, and is this payment acceptable?”
Agent delivery pre-authorization check
“Before my agent accepts this x402 payment request, check if any of the offered schemes ['exact/v1','erc20/v1'] are in my supported list ['erc20/v1','base/v1'] and give me a clear accept or reject decision.”
Multi-scheme compatibility filtering for buyer agent
“My buying agent received a challenge with schemes ['lightning/v1','evm/v1','exact/v1'] and supports only ['evm/v1']. Run the scheme selection and tell me which one was picked and any reasons if there's a mismatch.”
Technical details
Endpoint
POSThttps://api.delx.ai/api/v1/x402/x402-scheme-select?utm_source=zero.xyzWhen to prefer
Use this endpoint when implementing an x402 payment client or agent that needs to deterministically pick the correct payment scheme before authorizing or accepting a payment. It is the right choice when you have a list of schemes from a challenge response and a list of what your buyer supports, and you need a normalized, auditable selection decision without building the logic yourself. Prefer it over custom client-side logic when you need explicit mismatch reasons and a versioned JSON decision record for audit or debugging.
Side effects
- No matching scheme found between offered and supported lists — returns rejection status with mismatch reasons
- Empty schemes or supported_schemes arrays — may return rejection or empty selection
- Malformed scheme strings or oversized arrays exceeding 256-item limit — may return validation error
- Payment failure (insufficient USDC balance for $0.001 fee) — request not processed
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| schemes | array | Schemes supplied to X402 Scheme Select; used only for this bounded calculation and processed in memory without retention. |
| supported_schemes | array | Supported Schemes supplied to X402 Scheme Select; used only for this bounded calculation and processed in memory without retention. |
Output
Schema · Response
{
"type": "json",
"example": {
"result": {
"selected": "exact",
"supported": [
"exact"
]
},
"schema": "delx/util-x402-scheme-select/v1",
"status": "pass",
"evidence": {
"retained": false,
"input_sha256": "a045739927a7259d237f0c405b73130cd2fb17caabdca6ce41cffff6ac4ff2ed",
"external_calls": 0
},
"operation": "delivery_contract:x402_scheme_select"
}
}Tags
x402
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