<?php
 
$output = '{"Response":"<?xml version=\"1.0\" encoding=\"utf-8\"?><soap:Envelope xmlns:soap=\"http:\/\/schemas.xmlsoap.org\/soap\/envelope\/\" xmlns:xsi=\"http:\/\/www.w3.org\/2001\/XMLSchema-instance\" xmlns:xsd=\"http:\/\/www.w3.org\/2001\/XMLSchema\"><soap:Body><LeadEntryResponse xmlns=\"http:\/\/www.abc.com\/\"><LeadEntryResult><AFFILIATES_LEAD xmlns=\"\"><STATUS><LEAD_STATUS>REJECTED<\/LEAD_STATUS><REMARK> LEAD ALREADY EXSITS  - <\/REMARK><\/STATUS><\/AFFILIATES_LEAD><\/LeadEntryResult><\/LeadEntryResponse><\/soap:Body><\/soap:Envelope>"}';
$key = 'LEAD ALREADY EXSITS';
    //CODE
    if (strpos($output,$key) !== false)
     {
 
                         echo "success";
      } else {
      	echo "failure";
      }

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