The library help you to verify Admob callback in server.
composer require junthink/lumen-admob-ssv
use junthink\LaravelAdmobSsv\AdMob;
use Illuminate\Http\Request;
public function callback(Request $request) {
$adMob = new AdMob($request);
if ($adMob->validate()) {
// success
} else {
// failed
}
}