Contract and e-signature API

Authentication

Create a key in Settings → API and send it as a Bearer token. Keys are stored hashed and shown once. Free plan: 1 key and 50 calls every 30 days. Pro: unlimited calls, up to 10 keys. Every plan: 60 requests per minute.

Authorization: Bearer clk_…

Send a contract for signature

One call drafts it from a template and emails the signing link. Pass text instead of template to use your own wording; omit signers to keep a draft you finish in the app.

curl -X POST https://clinch.lumnika.com/api/v1/documents \
  -H "Authorization: Bearer clk_..." \
  -H "Content-Type: application/json" \
  -d '{
    "title": "Website redesign",
    "template": "web-design-contract",
    "signers": [{ "name": "Jamie Client", "email": "jamie@example.com" }],
    "deposit_cents": 50000
  }'

Issue an invoice with a pay link

curl -X POST https://clinch.lumnika.com/api/v1/invoices \
  -H "Authorization: Bearer clk_..." \
  -H "Content-Type: application/json" \
  -d '{
    "client_name": "Jamie Client",
    "client_email": "jamie@example.com",
    "currency": "usd",
    "items": [{ "description": "Design sprint", "quantity": 1, "unit_cents": 150000 }]
  }'

Endpoints

Base URL https://clinch.lumnika.com/api/v1. Errors are JSON: {"error":{"code","message"}}.

• GET/me

  Check the API key

• GET/documents

  List documents

• POST/documents

  Create a contract (and optionally send it for signature)

  Pass exactly one of `text` (your contract, paragraphs separated by blank lines) or `template` (a slug from /templates). With `signers` the contract is sent by email in the same call; without, it stays a draft you can edit in the app.

• GET/documents/{id}

  Get a document

• POST/documents/{id}/send

  Send a draft for signature

• GET/invoices

  List invoices

• POST/invoices

  Create an invoice with a pay link

• GET/clients

  List clients (everyone you sent a document to)

• GET/webhooks

  List webhook subscriptions

• POST/webhooks

  Subscribe a URL to events (Pro)

  Each delivery is a POST with JSON `{id, event, created_at, data}` and header `X-Clinch-Signature: t=<unix>,v1=<hex HMAC-SHA256(secret, t + '.' + body)>`.

• DELETE/webhooks/{id}

  Remove a webhook subscription

Webhooks

Subscribe with POST /webhooks or in Settings → Integrations (Pro). Events: contract.signed, invoice.paid, proposal.accepted, inquiry.created, booking.created. Each delivery is signed with X-Clinch-Signature: t=…,v1=HMAC-SHA256(secret, t.body).

AI agents: pay per contract with x402

No account and no API key: an agent sends a contract for signature for 0.5 USDC on Base per document. POST /api/x402/sign with {title, text, signers:[{name,email}], from_name, message?}: the first reply is an x402 v1 402 with the payment terms; resend with X-PAYMENT and you get 201 with each signer's sign_url and a free status_url. Content refused by moderation or a failed send is not charged. Catalog: GET /api/x402.

curl -X POST https://clinch.lumnika.com/api/x402/sign \
  -H "Content-Type: application/json" \
  -d '{"title":"Web Design Agreement","from_name":"Acme Studio","text":"Scope: ...\n\nPayment: ...","signers":[{"name":"Dana Lee","email":"dana@client.com"}]}'
# -> 402 {x402Version:1, accepts:[...]} ; pay and resend with X-PAYMENT -> 201 {sign_url, status_url}

No-code

Using n8n, Make or Zapier? Import the OpenAPI spec as an HTTP connection, or see the integration recipes.