ブロックチェーンRPC。
リアルタイムのイベント。
コストは、もっと小さく。

import crypto from 'node:crypto'

app.post('/hooks/rpcnode', express.raw({ type: '*/*' }), (req, res) => {
  // X-RpcNode-Signature: t=<unix seconds>,v1=<hex>
  const sig = Object.fromEntries(
    req.get('X-RpcNode-Signature').split(',').map((p) => p.split('=')),
  )
  const expected = crypto
    .createHmac('sha256', process.env.RPCNODE_WEBHOOK_SECRET)
    .update(`${sig.t}.${req.body}`)
    .digest('hex')
  const ok = sig.v1?.length === expected.length &&
    crypto.timingSafeEqual(Buffer.from(sig.v1), Buffer.from(expected))
  if (!ok) return res.sendStatus(401)

  const e = JSON.parse(req.body)
  if (e.type === 'payment_order' && e.event === 'paid') {
    fulfil(e.order_id, e.aml) // X-RpcNode-Delivery is the idempotency key
  }
  res.sendStatus(200) // anything but 2xx is retried
})

import Pusher from 'pusher-js'

const pusher = new Pusher('<api key id>', {
  wsHost: '<host from your cabinet>',
  forceTLS: true,
  cluster: 'rpcnode',
  // your server signs private channels with the key secret
  channelAuthorization: { endpoint: '/pusher/auth' },
})

pusher
  .subscribe('private-payments')
  .bind('payment_order', (e) => {
    if (e.event === 'paid') fulfil(e.order_id, e.aml)
  })