Expert Meta CAPI Server Side Tracking & Multi Domain Tracking with sGTM & GA4 Guide in 2026

				
					<script>
(function() {
  // Utility: Retrieve specific cookie value by name
  function getCookie(name) {
    var value = "; " + document.cookie;
    var parts = value.split("; " + name + "=");
    if (parts.length === 2) return parts.pop().split(";").shift();
    return '';
  }

  // Utility: Generate persistent Event ID for deduplication
  function generateEventID() {
    return 'id_md_' + Date.now() + '_' + Math.floor(Math.random() * 1000000);
  }

  // Utility: Extract URL query string parameters
  function getQueryParam(param) {
    var urlParams = new URLSearchParams(window.location.search);
    return urlParams.get(param) || '';
  }

  // Preserve fbclid from URL or Session Storage
  var currentFbclid = getQueryParam('fbclid');
  if (currentFbclid) {
    sessionStorage.setItem('x_fbclid', currentFbclid);
  } else {
    currentFbclid = sessionStorage.getItem('x_fbclid') || '';
  }

  // Retrieve current Meta cookie values
  var fbp = getCookie('_fbp');
  var fbc = getCookie('_fbc');

  // Decorate outbound links targeting Domain B
  document.addEventListener('click', function(e) {
    var anchor = e.target.closest('a');
    if (anchor && anchor.href) {
      var targetUrl = new URL(anchor.href, window.location.href);
      
      // Specify target cross-domain destinations
      if (targetUrl.hostname.indexOf('checkout-brand.com') !== -1 || targetUrl.hostname.indexOf('shopbrand.com') !== -1) {
        if (currentFbclid) targetUrl.searchParams.set('fbclid', currentFbclid);
        if (fbp) targetUrl.searchParams.set('meta_fbp', fbp);
        if (fbc) targetUrl.searchParams.set('meta_fbc', fbc);
        anchor.href = targetUrl.toString();
      }
    }

    // Capture e-commerce checkout clicks
    if (e.target.closest('.checkout-button, [name="checkout"], .btn-proceed-checkout')) {
      var eventId = generateEventID();
      window.dataLayer = window.dataLayer || [];
      window.dataLayer.push({
        'event': 'custom_initiate_checkout',
        'event_id': eventId,
        'fbp': fbp,
        'fbc': fbc || currentFbclid,
        'cross_domain_source': window.location.hostname
      });
    }
  });

  // Extract inbound decorated URL parameters on Domain B
  var inboundFbp = getQueryParam('meta_fbp');
  var inboundFbc = getQueryParam('meta_fbc');
  if (inboundFbp && !getCookie('_fbp')) {
    document.cookie = "_fbp=" + inboundFbp + "; path=/; domain=." + window.location.hostname + "; max-age=" + (90*24*60*60);
  }
  if (inboundFbc && !getCookie('_fbc')) {
    document.cookie = "_fbc=" + inboundFbc + "; path=/; domain=." + window.location.hostname + "; max-age=" + (90*24*60*60);
  }
})();
</script>