Как отловить регистрацию пользователя в момент оформления заказа

AddEventHandler("main", "OnBeforeUserRegister", "OnBeforeUserUpdateHandler");

function OnBeforeUserUpdateHandler(&$arFields)
{
   
   CModule::IncludeModule("sale"); 
 
   $UserId = $arFields['ID'];

   $db_sales = CSaleOrderUserProps::GetList(
           array("DATE_UPDATE" => "DESC"),
           array("USER_ID" => $UserId),
           false,
           array("nTopCount" => 1)   
       );

   $profileID = '';
       
   while ($ar_sales = $db_sales->Fetch())
       {
             $profileID = $ar_sales['ID'];   
       }

   $propsUser = array(
      'FIO' => 'NAME',
           'ZIP' => 'PERSONAL_ZIP',
           'LOCATION' => 'PERSONAL_CITY',
           'ADDRESS' => 'PERSONAL_STREET',  
           'PHONE' => 'PERSONAL_MOBILE',         
       );

   $fieldsUser = array();    
    
   // получим свойства профиля 
       $db_propVals = CSaleOrderUserPropsValue::GetList(($b="SORT"), ($o="ASC"), Array("USER_PROPS_ID"=>$profileID));
       while ($arPropVals = $db_propVals->Fetch())
       {
      foreach($propsUser as $key => $value) {
         if($arPropVals['CODE'] == $key && empty($arFields[$value])) {
            if($key == 'LOCATION') {
               $city_name = CSaleLocation::GetByID($arPropVals['VALUE'], LANGUAGE_ID);
               $arFields[$value] = $city_name['CITY_NAME'];
            } else {
               $arFields[$value] = $arPropVals['VALUE'];
            }
         }
    
      }
    
   }
   
      
 
       }  
   
   define("LOG_FILENAME", $_SERVER["DOCUMENT_ROOT"]."/tmp.txt");  
   AddMessage2Log(print_r($arFields, true)); 
        return $arFields;
   
}