Build billing in minutes, not weeks.
One REST API for GST-compliant invoices, customers, payments and webhooks. Native SDKs for Node and Python. Built for speed.
Quickstart
Live in 3 steps.
From sign-up to your first invoice in under five minutes.
Get your API key
Sign in to your dashboard and create a new secret key under Settings → API.
// Store your key in an environment variable
process.env.BILL21_API_KEY = "sk_live_••••••••";Install the SDK
Pick your language. Or skip and call the REST API directly with cURL.
npm install @21bill/node
# or
yarn add @21bill/nodeSend your first invoice
Create a GST-compliant invoice and email it to a customer in one call.
import Bill21 from "@21bill/node";
const bill = new Bill21(process.env.BILL21_API_KEY);
const invoice = await bill.invoices.create({
customer_id: "cus_8h2k",
items: [{ name: "Consulting", qty: 1, rate: 50000, gst: 18 }],
send_email: true,
});
console.log(invoice.id, invoice.pdf_url);API Reference
Endpoints, in plain English.
Every resource is a REST endpoint that returns predictable JSON. Authenticate with a bearer token. That's it.
Invoices
/v1/invoices Create a GST-compliant invoice. Returns a signed PDF URL and IRN.
await bill.invoices.create({
customer_id: "cus_8h2k",
items: [{ name: "Design sprint", qty: 1, rate: 120000, gst: 18 }],
due_date: "2025-05-01",
});/v1/invoices/:id Retrieve a single invoice by its ID.
const invoice = await bill.invoices.retrieve("inv_2k9f");/v1/invoices List invoices with filters: status, customer, date range.
const { data } = await bill.invoices.list({ status: "unpaid", limit: 50 });Customers
/v1/customers Create a customer with billing address and GSTIN.
await bill.customers.create({
name: "Acme Pvt Ltd",
email: "ap@acme.in",
gstin: "29AAACB1234F1Z5",
});/v1/customers/:id Retrieve a customer with their full ledger summary.
const customer = await bill.customers.retrieve("cus_8h2k");Payments
/v1/payments Record a payment received against one or many invoices.
await bill.payments.create({
invoice_id: "inv_2k9f",
amount: 50000,
method: "upi",
reference: "UPI/REF/00123",
});/v1/payments List all payments, filterable by date or invoice.
const { data } = await bill.payments.list({ from: "2025-01-01" });Webhooks
React to billing events in real time.
We sign every payload with HMAC-SHA256 so you can trust what hits your server. Subscribe to one or many event types.
invoice.createdinvoice.sentinvoice.paidinvoice.overduecustomer.createdpayment.receivedpayment.failed // Express endpoint that verifies a 21bill signature
import crypto from "crypto";
app.post("/webhooks/21bill", (req, res) => {
const sig = req.headers["x-21bill-signature"] as string;
const expected = crypto
.createHmac("sha256", process.env.BILL21_WEBHOOK_SECRET!)
.update(JSON.stringify(req.body))
.digest("hex");
if (sig !== expected) return res.status(400).end();
const event = req.body;
if (event.type === "invoice.paid") {
// mark order as paid
}
res.json({ received: true });
});Ready to ship?
Grab a key and send your first invoice in under five minutes. Need help integrating? Our team replies within an hour.