use WebPush\Payload\AES128GCM;
use WebPush\Payload\AESGCM;
use WebPush\Payload\PayloadExtension;
$aes128gcm = new AES128GCM();
$aes128gcm->maxPadding();
$payloadExtension = new PayloadExtension();
$payloadExtension->addContentEncoding($aesgcm);
$payloadExtension->addContentEncoding($aes128gcm);