FastPay API documentation

Accept crypto on your website or Telegram bot: ten currencies across seven networks, prices always in USD, one hosted checkout and one signed webhook — plus a no-code path with payment links. All requests and responses are JSON over HTTPS.

Getting API keys

1. Create a free account — only an email is needed.
2. Open Business → + New merchant and connect your website or Telegram bot.
3. Websites confirm domain ownership with a DNS TXT record, a meta tag or a file — any one of the three.
4. After a quick review your merchant becomes Active and the API key starts working.

The fpk_… key is shown once at creation. Store it on your server — never expose it in browser code. A lost key can be regenerated in the merchant card at any time; the previous key is revoked immediately. The webhook secret for signature checks lives in the same card.

Request format

Send the API key in the Authorization header on every request. Only merchants in the Active status can call the API.

Authorization: Bearer fpk_your_api_key
Content-Type: application/json

Successful responses return HTTP 200 with a JSON body. Errors return a matching 4xx/5xx status and a JSON object with a single error field — see Errors & limits.

Payments — getting started

The flow is the same for a website and a bot:

1. Create an invoice from your backend when the customer checks out.
2. Redirect the customer to the returned url — the hosted FastPay checkout.
3. The customer picks a currency (USDT, USDC, DAI, BNB, ETH, SOL, TON, TRX, POL, AVAX) and network, then sends the exact amount shown on the checkout.
4. We detect the transfer on-chain, credit your Business balance minus the service fee and mark the invoice paid.
5. Your server gets a signed webhook — or you poll the invoice status.

Set a Support URL in your merchant card: a customer whose payment fell short sees it on the checkout together with the payment ID, so they can reach you instead of guessing.

Who pays the service fee is your choice per merchant — My business (deducted from the credit) or Customer (added on top at checkout). Switch it in the merchant card.

Create an invoice

curl -X POST https://fast-pay.money/api/v1/invoice \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "amount": 20,
    "order_id": "ORDER-1001",
    "description": "Premium plan",
    "return_url": "https://yourstore.com/thanks"
  }'

{
  "invoice": {
    "uuid": "6e249771-4ced-4a9d-9c67-2efb1876070f",
    "url": "https://fast-pay.money/pay/6e249771-4ced-4a9d-9c67-2efb1876070f",
    "status": "pending",
    "amount": "20.00",
    "currency": "USD",
    "order_id": "ORDER-1001",
    "expires_at": "2026-07-25 05:08:16",
    "created_at": "2026-07-25 04:08:16"
  }
}

Redirect your customer to url. The invoice stays payable for 60 minutes by default; the exact deadline is always in expires_at.

Invoice information

curl "https://fast-pay.money/api/v1/invoice?uuid=6e249771-4ced-4a9d-9c67-2efb1876070f" \
  -H "Authorization: Bearer YOUR_API_KEY"

{
  "invoice": {
    "status": "paid",
    "asset": "USDT",
    "network": "bep20",
    "payment_amount": "20.00",
    "paid_amount": "20.00",
    "fee": "0.10",
    "tx_hash": "0xc267…a02c",
    "paid_at": "2026-07-25 04:12:31"
  }
}

Amount formats: stablecoins are quoted with 2 decimals, other coins with 8. tx_hash is null for balance-detected coins.

Payment statuses

Alongside status, every invoice and every webhook carries payment_status — a detailed code meant for automated handling. It distinguishes cases that status merges:

Credit only on paid and paid_over. An underpayment never produces a paid event, so a platform that cannot credit partial amounts needs no special handling: it simply ignores everything else and waits for the customer's top-up, which arrives as a normal paid event for the same uuid.

A transfer that arrives with a wrong amount, in a different coin or after the grace window is still credited to your Business balance as a plain deposit — customer funds are never dropped. See Underpayments & edge cases for the exact rules.

Underpayments & edge cases

Real customers pay from exchanges and custodial wallets that may deduct their own fee from the sum, send late or pick the wrong coin. The rules below are deterministic; no payment is ever lost.

Plain deposits are visible in your Business transaction history with the sending transaction hash, so any disputed payment can be traced on-chain.

Webhooks

Set the Webhook URL in your merchant card. We POST a JSON event when an invoice is paid, when a payment arrives but falls short (status: "underpaid") and when the invoice expires unpaid (status: "expired", sent after the 30-minute late-payment grace window closes). All three share one shape. A paid event looks like this:

{
  "type": "payment",
  "uuid": "6e249771-4ced-4a9d-9c67-2efb1876070f",
  "order_id": "ORDER-1001",
  "status": "paid",
  "amount": "20.00",
  "payment_amount": "20.0000",
  "paid_amount": "20.0000",
  "asset": "USDT",
  "network": "bep20",
  "tx_hash": "0xc267…a02c",
  "fee": "0.1000",
  "test": false,
  "merchant_id": "21aef00c-6ccf-4f7b-a623-4668ce5af5ac",
  "paid_at": "2026-07-25 04:12:31"
}

Every delivery is signed: the X-FastPay-Signature header is the hex HMAC-SHA256 of the raw request body, keyed with your webhook secret. Always verify it:

// Node.js
const crypto = require('crypto');

function isValidWebhook(rawBody, signatureHeader, webhookSecret) {
  const expected = crypto.createHmac('sha256', webhookSecret)
    .update(rawBody).digest('hex');
  const got = Buffer.from(signatureHeader || '', 'hex');
  const want = Buffer.from(expected, 'hex');
  // Lengths must match before comparing — timingSafeEqual throws otherwise,
  // and a forged or missing signature is exactly the mismatched case.
  if (got.length !== want.length) return false;
  return crypto.timingSafeEqual(got, want);
}

<?php // PHP
function is_valid_webhook(string $rawBody, string $signature, string $secret): bool {
    return hash_equals(hash_hmac('sha256', $rawBody, $secret), $signature);
}

received_amount is the total received for this invoice so far and remaining_amount is what is still missing — both are present on every event, which is all you need to handle an underpaid notification: hold the order, tell the customer, or credit them partially. A later top-up produces a paid event for the same uuid. Both figures are in the coin the customer is paying with; the same two values in USD arrive as received_amount_usd and remaining_amount_usd, converted at the rate locked when the customer picked the currency — so a short payment in LTC or BTC can be read in dollars without fetching a rate yourself. They are null until a currency is picked.

amount is the invoice face value in USD; payment_amount, paid_amount and fee are in the currency from asset. tx_hash can be null for coins settled by balance detection (BNB, ETH, POL, AVAX, SOL) — do not require it.

Respond with any 2xx to acknowledge. If your endpoint is down we retry with growing delays from a durable queue, and you can resend any webhook manually from the payment card in the dashboard. Deliveries can arrive more than once — treat the invoice uuid as your idempotency key.

Testing

Pass "test": true when creating an invoice to get a test invoice: the checkout shows a TEST MODE banner and a «Simulate payment» button instead of waiting for a real transfer. Pressing it flips the invoice to paid and delivers a normal signed webhook with "test": true — no money and no balances move anywhere.

curl -X POST https://fast-pay.money/api/v1/invoice \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "amount": 5, "order_id": "TEST-1", "test": true }'

To verify webhook delivery before your own endpoint is ready, set the merchant's Webhook URL to https://fast-pay.money/webhook-echo: it accepts the POST, answers 200 and stores nothing. The delivery status is visible on the payment card in the dashboard.

Always check the test field in your webhook handler and skip crediting when it is true. Test invoices are excluded from your income stats. For an end-to-end rehearsal with real money, any live invoice from $0.50 works — or try the flow yourself at the demo shop.

Playground

Try the API right here. Paste your API key (Business → merchant card), create a test invoice and walk the whole flow — the «Simulate payment» button on the checkout completes it and delivers your webhook with test: true. The key stays in your browser only.

Payment links

Payment links accept payments without any integration. Create a fixed-amount payment page in Business → Payment links and share the URL anywhere — chat, e-mail, social. Every click mints a fresh invoice, so any number of customers can pay the same link at the same time. Toggle a link off and it stops working instantly.

Payments made through links appear in the same Payments list and send the same webhooks as API invoices.

Refunds

curl -X POST https://fast-pay.money/api/v1/invoice/refund \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "uuid": "6e249771-4ced-4a9d-9c67-2efb1876070f" }'

{
  "refund": { "withdrawal_id": "b0c1…", "amount": "19.54", "fee": "0.50", "status": "requested" }
}

The amount you were credited for the invoice is debited from your Business balance; the payer receives it minus the network payout fee. Refunds go out after a quick review, one refund per invoice. Currently available for USDT payments on TRC-20, BEP-20 and Polygon; the same button lives on the payment card in Business → Payments. refund_status on the invoice moves requested → sent; a rejected refund returns the money to your balance and lets you retry.

Payouts

Withdraw USDT from your balance to any external address on TRON (TRC-20), BSC (BEP-20) or Polygon: dashboard → Personal → Send. Business income moves to Personal with the free internal transfer first.

1. Enter the address — the network is detected from its format.
2. Review the per-network fee and confirm. The amount plus the fee is reserved from your balance.
3. Every payout is individually reviewed, then sent on-chain. You get notifications at each step, and the tx hash appears in your request list.
4. If a payout is rejected or fails, the full reserved amount returns to your balance automatically.

Current limits and per-network fees are shown right in the Send form.

Supported currencies & networks

Invoices are always created in USD. On the checkout the customer picks what to pay with; you are credited in the currency they paid.

There is no business minimum — invoices are accepted from the $0.01 accounting floor; per-shop minimums are your own policy. * Non-stablecoin rates come from the live market and are locked for the invoice lifetime (60 minutes by default, see expires_at). Coin amounts are calculated to eight decimals, the precision the chains themselves use, and the exact figure is shown to the customer before they pay. The wallet holds 16 coins across 9 chains for deposits and storage; BTC and LTC on the checkout are next.

Exchange rates

Returns indicative USD market rates for every supported currency. Stablecoins are pinned to 1. The rate applied to an invoice is locked at the moment the customer picks the currency and held for the invoice lifetime; this endpoint is for display purposes on your side.

curl "https://fast-pay.money/api/v1/exchange-rates" \
  -H "Authorization: Bearer YOUR_API_KEY"

{
  "base": "USD",
  "rates": {
    "USDT": "1.00000000",
    "USDC": "1.00000000",
    "DAI": "1.00000000",
    "BNB": "567.33000000",
    "ETH": "1869.17000000",
    "POL": "0.08000000",
    "AVAX": "6.54000000",
    "TRX": "0.33000000",
    "SOL": "74.20000000",
    "GRAM": "1.60000000"
  }
}

Errors & limits

Every error is returned as JSON with an HTTP status and a single human-readable error field:

{ "error": "amount must be between 0.01 and 100000 USD" }

From $0.01 to $100 000 per invoice. Need a higher ceiling? Ask us.

Legal

Using the API means you accept our terms:

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