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