┌─────────────────────────┐
 │ 1. Level exists in the   │  ← one-time, done in dashboard or
 │    workspace              │     via sumsub-create-level
 └─────────────┬───────────┘
               │ levelName
 ┌─────────────▼───────────┐  ┌──────────────────────────────────┐
 │ 2. Server-side token     │◀─┤ Browser calls /api/sumsub/token │
 │    endpoint (HMAC-signed │  └──────────────────────────────────┘
 │    POST /resources/      │
 │    accessTokens)         │
 └─────────────┬───────────┘
               │ {token, userId}
 ┌─────────────▼───────────┐
 │ 3. Browser: snsWebSdk    │  ← user fills doc capture / selfie / form
 │    init → build → launch │     events fire: onApplicantSubmitted, etc.
 └─────────────┬───────────┘
               │ documents submitted
 ┌─────────────▼───────────┐  ┌──────────────────────────────────┐
 │ 4. Sumsub runs checks    │─▶│ Webhook POST → your server      │
 │    (async, ~seconds–min) │  │ (applicantReviewed = the truth) │
 └─────────────┬───────────┘  └──────────────────────────────────┘
               │ verdict
 ┌─────────────▼───────────┐
 │ 5. Your app gates access │  ← server checks reviewAnswer, not
 │    by reading applicant  │     the browser. Browser events are
 │    via GET /applicants…  │     UX only.
 └─────────────────────────┘

POST https://api.sumsub.com/resources/accessTokens
  ?userId=<your-stable-user-id>
  &levelName=<level-from-stage-1>
  &ttlInSecs=600

SUMSUB_APP_TOKEN='sbx:...'
SUMSUB_SECRET_KEY='...'
USER_ID='u-12345'
LEVEL='basic-kyc-level'

PATH_Q="/resources/accessTokens?userId=${USER_ID}&levelName=${LEVEL}&ttlInSecs=600"
TS=$(date -u +%s)
SIG=$(printf '%s%s%s' "$TS" "POST" "$PATH_Q" \
      | openssl dgst -sha256 -hmac "$SUMSUB_SECRET_KEY" -hex \
      | awk '{print $NF}')

curl -sS -X POST \
  -H "X-App-Token: $SUMSUB_APP_TOKEN" \
  -H "X-App-Access-Ts: $TS" \
  -H "X-App-Access-Sig: $SIG" \
  "https://api.sumsub.com${PATH_Q}"

<script src="https://static.sumsub.com/idensic/static/sns-websdk-builder.js"></script>

<div class="kyc-stage" style="position: relative; min-height: 600px;">
  <div id="sumsub-websdk-container"></div>
  <!-- Overlay loader covers the empty-iframe window. Hide on idCheck.onReady. -->
  <div id="kyc-loader" style="position: absolute; inset: 0; display: grid; place-items: center;">
    Loading verification…
  </div>
</div>

async function getAccessToken() {
  const r = await fetch('/api/sumsub/access-token', { method: 'POST' });
  if (!r.ok) throw new Error('failed to mint access token');
  return (await r.json()).token;
}

const initialToken = await getAccessToken();

const sdk = snsWebSdk
  .init(initialToken, () => getAccessToken())   // refresh callback, returns Promise<string>
  .withConf({
    lang: 'en',
    email: currentUser.email,                   // optional, prefills
    phone: currentUser.phone,                   // optional, prefills
    theme: 'light',                             // 'light' | 'dark'
  })
  .withOptions({
    addViewportTag: false,                      // host page already sets it
    adaptIframeHeight: true,
  })
  .on('idCheck.onReady', () => {
    // SDK iframe content loaded — hide the overlay loader from the container snippet.
    document.getElementById('kyc-loader')?.style.setProperty('display', 'none');
  })
  .on('idCheck.onApplicantSubmitted', () => {
    // user just finished uploading; show "we're reviewing"
  })
  .on('idCheck.onApplicantStatusChanged', (payload) => {
    // status moved; payload.reviewStatus = 'pending' | 'queued' | 'completed' | ...
  })
  .on('idCheck.onError', (err) => {
    console.error('sumsub error', err);
  })
  .onMessage((type, payload) => {
    // catch-all firehose — useful for analytics or debugging
  })
  .build();

sdk.launch('#sumsub-websdk-container');

// Node/Express — bodyParser.raw() so req.body is a Buffer
import crypto from 'node:crypto';

const ALG = { HMAC_SHA1_HEX: 'sha1', HMAC_SHA256_HEX: 'sha256', HMAC_SHA512_HEX: 'sha512' };

function verifySumsubWebhook(req, secret) {
  const alg = ALG[req.header('x-payload-digest-alg') || 'HMAC_SHA256_HEX'];
  const expected = req.header('x-payload-digest');
  const actual = crypto.createHmac(alg, secret).update(req.body).digest('hex');
  return Buffer.from(actual, 'hex').length === Buffer.from(expected, 'hex').length
      && crypto.timingSafeEqual(Buffer.from(actual, 'hex'), Buffer.from(expected, 'hex'));
}

undefined

`webhook.site` works too if you just want to see the raw payload without
running a local receiver — but it can't echo back a `200` to verify the
delivery flow.

PATH_Q="/resources/applicants/${USER_ID}/one"
TS=$(date -u +%s)
SIG=$(printf '%s%s%s' "$TS" "GET" "$PATH_Q" \
      | openssl dgst -sha256 -hmac "$SUMSUB_SECRET_KEY" -hex \
      | awk '{print $NF}')

curl -sS \
  -H "X-App-Token: $SUMSUB_APP_TOKEN" \
  -H "X-App-Access-Ts: $TS" \
  -H "X-App-Access-Sig: $SIG" \
  "https://api.sumsub.com${PATH_Q}"