/**
  * Get list of people who have been removed from the subscribed list and have tried to re-subscribe
  *
  * @param string $client_id 
  * @return void
  * @author Dan Chadwick
  */
 public function get_suppression_list($client_id = null)
 {
     $client_id = $client_id == null ? $this->client_id : $client_id;
     $cm = new CampaignMonitor($this->api_key);
     // Optional statement to include debugging information in the result
     $cm->debug_level = 1;
     // This is the actual call to the method
     $result = $cm->clientGetSuppressionList($client_id);
     return $result;
 }
<?php

ini_set('display_errors', 1);
error_reporting(E_ALL);
require_once 'CMBase.php';
//-----------------------------INPUT PARAMS---------------------------------------
$apikey = 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx';
$client_id = 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx';
//-------------------------------------------------------------------------------
$cm = new CampaignMonitor($apikey);
//Optional statement to include debugging information in the result
$cm->debug_level = 1;
//This is the actual call to the method
$result = $cm->clientGetSuppressionList($client_id);
echo '<br><br>';
print_r($result);