Fax server steps

hello everyone. i do have freepbx running in my debian server. all connections to outside world are IP trunks, there is no extra card for voice in the system. i am trying to setup a fax server and i have bumped to some problems.
As for getting it working, it’s quite straightforward.
i have followed the following steps:
1.) add postfix to the system and use my gmail account to send emails from the system.
2.) Create an IAX extension.
3.) Install IAXModem and configure for that extension.
4.) Install HylaFAX and setup to use IAXModem.
5.) Setup FaxDispatch to send faxes to where you want them.

unfortunatelly i cannot send/receive any faxes.

there is something messed up somewhere but i cannot see where. Is there a detailed instruction on how to setup, to avoid the errors, please?