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Google Ads parallel tracking: follow em_dest, then 204

Under Google Ads parallel tracking, shoppers go to the campaign Final URL. This measurement URL is loaded in the background. If that request carries a valid em_dest, the server follows it with an empty server-side 302—any User-Agent, including Google-Ads-Compliance. That is the published transparency rule.

A Google-Ads-Compliance request with no followable hop returns 204 No Content: empty body, no cookies, no click_events write. Humans with a missing or invalid hop receive empty HTTP 400. We never 302 those requests to this host.

// Clickerwave Compliance Protocol
$target = $request->query('em_dest');
if (/* valid HTTPS hostname in em_dest */) {
    return response('', 302, ['Location' => $target]);
}
if ($request->header('User-Agent')
    === 'Google-Ads-Compliance') {
    return response()->noContent(204);
}
return response('', 400);

Deployed logic matches this snippet. Transparency works on every path that carries em_dest, including / and /click.