- simplexml_load_string: documentation ( source)
<?php
$xml = "<?xml version='1.0' encoding='utf-8'?><merchant><merchantID>33abc947-f7d5-45f7-9b99-6825b72b74db</merchantID></merchant><transaction><merchantTransactionID>123456</merchantTransactionID><method>boleto</method><customerName>João Silva</customerName><CPF>36874950860</CPF><currency>BRL</currency><value>10000</value></transaction>";
$ler = simplexml_load_string($xml);
echo 'teste<br>';
echo $ler->merchantID;
?>