use magic const __DIR__ in require_once

zimbraAddressAvailable.php

@@ -19,8 +19,8 @@ if($pos===false) {
  * Requires this PHP api to make soap calls and parse responses
  */
 require_once(__DIR__ . '/../../../init.php');
-require_once('api/Zm/Auth.php');
-require_once('api/Zm/Account.php');
+require_once(__DIR__ . '/api/Zm/Auth.php');
+require_once(__DIR__ . '/api/Zm/Account.php');
 use WHMCS\Database\Capsule;
 
 $whmcs = App::self();

zimbraSingle.php

@@ -20,10 +20,10 @@ use WHMCS\Database\Capsule;
  * This is an extend version of:
  * @see https://github.com/alloylab/zimbra-admin-api-soap-php
  */
-require_once('api/Zm/Auth.php');
-require_once('api/Zm/Account.php');
-require_once('api/Zm/Domain.php');
-require_once('api/Zm/Server.php');
+require_once(__DIR__ . '/api/Zm/Auth.php');
+require_once(__DIR__ . '/api/Zm/Account.php');
+require_once(__DIR__ . '/api/Zm/Domain.php');
+require_once(__DIR__ . '/api/Zm/Server.php');
 
 /**
  * Helper function to find values of a named key in a multidimensional arrays or objects