Node.js Example: Creating an Invoice

Run this code on a trusted server. Never expose the merchant API key in browser JavaScript.

const crypto = require('node:crypto')

function canonicalJson(payload) {
  return JSON.stringify(payload)
    .replace(/\//g, '\\/')
    .replace(/[\u0080-\uFFFF]/g, character =>
      `\\u${character.charCodeAt(0).toString(16).padStart(4, '0')}`
    )
}

function legacySign(body, apiKey) {
  const payloadBase64 = Buffer.from(body, 'utf8').toString('base64')
  return crypto.createHash('md5').update(payloadBase64 + apiKey).digest('hex')
}

async function createInvoice({ merchantId, apiKey, orderId, amount }) {
  const payload = {
    order_id: orderId,
    amount,
    is_customer_fee: false,
    is_customer_network_fee: false,
    allow_card_payments: true,
    success_url: 'https://merchant.example/payment-success',
    cancel_url: 'https://merchant.example/payment-cancelled'
  }
  const body = canonicalJson(payload)

  const response = await fetch('https://api.coinssend.com/v1/invoices', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      Merchant: merchantId,
      Sign: legacySign(body, apiKey)
    },
    body
  })

  const result = await response.json()
  if (!response.ok) {
    throw new Error(result.error || result.message || `HTTP ${response.status}`)
  }

  return result.data
}

const invoice = await createInvoice({
  merchantId: process.env.COINSSEND_MERCHANT_ID,
  apiKey: process.env.COINSSEND_API_KEY,
  orderId: `order_${Date.now()}`,
  amount: '100.50'
})

console.log(invoice.code, invoice.url)

Persist id, order_id, code, and url before redirecting the buyer. If the request outcome is unknown, do not generate a new order ID and retry blindly. A repeated accepted order_id returns 409 without replaying the original invoice response.