Integrating WHMCS with Hosting Controller

We are using Hosting Controller for Microsoft Exchange Hosting. Now we have planned to integrate HC with WHMCS which has been done successfully.
 
 
The only problem (may be or may be not) is when i try to create an order for exchange organization from WHMCS, it says "Organization created successfully, failed to create exchange mail-domain".
 
Do you have any idea what am I doing wrong here ???

There is no issue with WHMCS and Exchange module. You can check by creating OU and Mail Domain via HC panel which will reveal to you the root cause of the issue and to rectify it by taking necessary actions.