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x402 Signature Service — E-Signatures for AI Agents
x402
x402 Signature Service — E-Signatures for AI Agents is a paid API for AI agents from signx402.com, paid per call via x402, $0.5/call, status unknown (last checked 2026-09-15).
Sends a PDF document to an email recipient for electronic signature, returns a tracking token and status URL, and enables status polling and signed PDF retrieval.
Price / call$0.5
Success—
StatusUnknown
How this service works
Pay-per-call API (x402, $0.50 USDC on Base): send one PDF to one email recipient for simple electronic signature, track status, download the signed PDF.
Output
Returns a JSON object with a unique signature request ID (e.g. sigreq_…), signer details (name and masked email), current status ('sent'), creation and expiry timestamps, a statusUrl for polling the request status, a one-time plain-text access token for downstream management calls, and the document name.
Example use cases
Contractor agreement signing
“Send this contractor agreement PDF at https://files.mycompany.com/contractor-agreement.pdf to Sarah Chen at sarah.chen@freelancer.io for her signature — call it 'Contractor Services Agreement', add the message 'Hi Sarah, please sign at your earliest convenience', and give her 10 days before it expires.”
Client onboarding signature
“I need a new client to sign our onboarding terms — send the PDF from https://legal.mybiz.com/onboarding-terms.pdf to Marcus Webb at m.webb@clientco.com, title it 'Client Onboarding Agreement', and let them know they have 14 days to sign it.”
Vendor NDA collection
“Request a signature on our standard vendor NDA — the PDF is base64-encoded, signer is Priya Sharma at priya@vendorcorp.net, name the document 'Vendor Non-Disclosure Agreement', include the message 'Please sign before our kickoff call', and set expiry to 5 days.”
Technical details
Endpoint
GEThttps://signx402.com/v1/signature-requestsWhen to prefer
Choose this endpoint when an AI agent needs to automate the e-signature step of a document workflow on a pay-per-call basis with no subscription required — particularly suited for agentic pipelines where cost predictability ($0.50 USDC flat per request) matters and the use case is one PDF to one email recipient. Prefer this over subscription-based e-sign platforms when volume is low or unpredictable, or when the agent must handle payment natively via the x402 protocol on Base.
Side effects
- Invalid or unreachable documentUrl returns an error (PDF could not be fetched)
- PDF exceeds 5 MB size limit causes rejection
- Invalid signer email format triggers validation error
- Missing required fields (signer name, email, document source) returns 400-level error
- Payment not completed via x402 protocol results in 402 Payment Required response
- Both documentUrl and documentBase64 provided simultaneously may cause conflict error
- expiresInDays outside range 1–30 triggers validation error
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| signer | object | |
| message | string | Optional message included in the signature request email |
| documentUrl | string | HTTPS URL of the PDF to sign (max 5 MB). Provide either documentUrl OR documentBase64. |
| documentName | string | Human-readable document title shown to the signer |
| expiresInDays | integer | Days until the signature request expires |
| documentBase64 | string | Base64-encoded PDF (max 5 MB decoded). Provide either documentUrl OR documentBase64. |
| externalReference | string | Optional caller-side reference id, echoed back in responses |
Output
Schema · Response
{
"type": "json",
"example": {
"id": "sigreq_1f4a9c2b7d3e8a01",
"signer": {
"name": "Anna Müller",
"email": "a***@example.com"
},
"status": "sent",
"createdAt": "2026-07-19T15:00:00Z",
"expiresAt": "2026-08-02T15:00:00Z",
"statusUrl": "https://your-api.example.com/v1/signature-requests/sigreq_1f4a9c2b7d3e8a01",
"accessToken": "sec_… (plain-text bearer token, shown exactly once)",
"documentName": "Service Agreement"
}
}Tags
x402
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