SmoothSign
    Agent API · v1

    Agent API

    A self-service HTTP API designed for AI agents (Claude, ChatGPT, Grok, Cursor, custom LLM tools) to send documents for legally binding e-signatures. No human onboarding required — register programmatically, top up a prepaid balance via Stripe, and start sending.

    For LLM crawlers / agents that can't execute JavaScript, a plain-text version of this page is available at /agents/api.md and a full machine-readable index at /llms-full.txt.

    $0.75 USD
    per signature (25% off $1.00)
    3 modes
    prepaid · auto-charge · per-call token
    No human
    in the loop
    Currency: All amounts are in USD cents. pricePerSignatureCents: 75 means $0.75 USD per signature — not 75 NOK øre. Stripe top-ups and charges are processed in usd.

    Billing modes

    prepaid (default)

    Top up via Stripe Checkout. Each signature is debited from the balance. Best when the agent operates without a human nearby and you want a hard spend cap.

    auto_charge

    A human saves a card once via POST /agent-setup-card. Every /agent-send-document creates a Stripe PaymentIntent off-session for the exact cost. No top-ups, no balance — just pay-as-you-go.

    per_call_token

    The caller supplies a Stripe paymentMethodId (or sharedPaymentToken) on every request. Designed for agents that hold their own Stripe Issuing card or Link Shared Payment Token per transaction.

    Quick start

    1. Register your agent and receive an API key.
    2. Create a Stripe Checkout session to add credit. Open the URL in a browser to pay with a card.
    3. Send documents — each signature debits the current per-signature price (25% off our standard rate; call GET /agent-balance to see the live pricePerSignatureCents) from your balance.

    1. Register

    POST https://ueurrqgdjcpdzflvgbaz.supabase.co/functions/v1/agent-register

    curl -X POST https://ueurrqgdjcpdzflvgbaz.supabase.co/functions/v1/agent-register \
  -H "Content-Type: application/json" \
  -d '{"name": "Acme Sales Bot", "contactEmail": "ops@acme.com"}'

    Returns { agentId, apiKey, prefix, ... }. Save the apiKey immediately — it is shown only once.

    2. Create a top-up

    POST https://ueurrqgdjcpdzflvgbaz.supabase.co/functions/v1/agent-create-topup

    curl -X POST https://ueurrqgdjcpdzflvgbaz.supabase.co/functions/v1/agent-create-topup \
  -H "Authorization: Bearer ssk_live_..." \
  -H "Content-Type: application/json" \
  -d '{"amountCents": 5000}'

    Returns { checkoutUrl, sessionId }. The agent's owner opens the URL and pays with a card. Balance is credited automatically once the payment succeeds.

    3. Send a document

    POST https://ueurrqgdjcpdzflvgbaz.supabase.co/functions/v1/agent-send-document

    curl -X POST https://ueurrqgdjcpdzflvgbaz.supabase.co/functions/v1/agent-send-document \
  -H "Authorization: Bearer ssk_live_..." \
  -H "Content-Type: application/json" \
  -d '{
    "signers": ["alice@example.com", "bob@example.com"],
    "message": "Please sign the NDA",
    "files": [{ "name": "nda.pdf", "base64": "JVBERi0xLjQK..." }]
  }'

    Each signer is charged once per file. Returns 402 Payment Required if balance is insufficient. On success returns { sent, balanceCents, results }.

    4. Check balance

    GET https://ueurrqgdjcpdzflvgbaz.supabase.co/functions/v1/agent-balance

    curl https://ueurrqgdjcpdzflvgbaz.supabase.co/functions/v1/agent-balance \
  -H "Authorization: Bearer ssk_live_..."

    Returns { balanceCents, signaturesRemaining, recentLedger }.

    5. (auto_charge) Save a card

    POST https://ueurrqgdjcpdzflvgbaz.supabase.co/functions/v1/agent-setup-card

    curl -X POST https://ueurrqgdjcpdzflvgbaz.supabase.co/functions/v1/agent-setup-card \
  -H "Authorization: Bearer ssk_live_..." \
  -H "Content-Type: application/json" -d '{}'

    Returns { checkoutUrl }. A human opens the URL once, saves a card, and the agent can then run in auto_charge mode without ever topping up.

    6. Switch billing mode

    POST https://ueurrqgdjcpdzflvgbaz.supabase.co/functions/v1/agent-billing-config

    curl -X POST https://ueurrqgdjcpdzflvgbaz.supabase.co/functions/v1/agent-billing-config \
  -H "Authorization: Bearer ssk_live_..." \
  -H "Content-Type: application/json" \
  -d '{"billingMode": "auto_charge"}'

    Modes: prepaid, auto_charge (requires saved card), per_call_token (requires paymentMethodId or sharedPaymentToken on every request).

    Errors

    • 401 — invalid or missing API key
    • 402 — insufficient balance, missing/declined payment method, or missing per-call token
    • 403 — agent has been deactivated
    • 409 — cannot enable auto_charge without a saved card
    • 429 — registration rate limit
    • 207 — partial success when sending multiple files

    Notes for LLM tool builders

    • The API key acts as a Bearer token — store it in a secret manager.
    • If you receive 402 in prepaid mode, call agent-create-topup and surface the checkout URL to a human.
    • If you receive 402 in auto_charge mode, the saved card was declined — surface to the human and re-run agent-setup-card.
    • PDFs must be base64-encoded (no data: prefix), max 15MB each, max 10 files per call.
    • Up to 50 signers per document.