op_return.php

<?php
$ec = Bitcoin::getEcAdapter();
$key = PrivateKeyFactory::fromWif('YOUR_WIF');

$outpoint = new OutPoint(Buffer::hex('YOUR_TRANSACTION', 32), 0);

$scriptPubKey = ScriptFactory::scriptPubKey()->payToPubKeyHash($key->getPublicKey());

$value = 0;

$txOut = new TransactionOutput($value, $scriptPubKey);

$op = new Opcodes();

$destination = new WitnessProgram(0, $key->getPubKeyHash());

$sh = ScriptFactory::sequence([Opcodes::OP_RETURN, Buffer::hex('WHAT YOU WANT TO SEND']);

$p2sh = new \BitWasp\Bitcoin\Script\P2shScript($destination->getScript(), $op);

$tx = TransactionFactory::build()
      ->spendOutPoint($outpoint)
      ->payToAddress($txref['value'], AddressFactory::fromString($key->getPublicKey()->getAddress()->getAddress()))
      ->output(0, $sh)
      ->get();
      
$signed = new \BitWasp\Bitcoin\Transaction\Factory\Signer($tx, $ec);
$signed->sign(0, $key, $txOut);
$ss = $signed->get();