You don't send a fax to the ATA. You send it to FPL's voicemail. Let FPL's voicemail pick up the fax call.
If you want to send faxes with your ATA...
For faxing with an OBi200/202 (and FPL),
1) Use firmware 3.1.0 (Build: 5110): http://fw.obihai.com/OBi202-3-1-0-5110.fw (also works with OBi200)
2) If you used the Obitalk web portal (www.obitalk.com) to configure your ATA, keep in mind that you must continue using it to configure your ATA. Otherwise whatever settings you change will eventually be overwritten by what you previously entered at obitalk.com anyway. If you wish to disable this behaviour, dial ***1. Enter that IP address into a web browser. Navigate to System Management-->OBiTalk Provisioning-->select Disabled for the method. Save. Reboot ATA. Now obitalk.com won't overwrite whatever changes you make via the device's interface (via IP address).
Pick one method (obitalk.com) or the other (IP address of device) for changing device settings. But do not use both methods. Keep in mind that activating Google Voice requires using the Obitalk.com web portal.
3) Navigate to Codecs-->Codec Profile (A or whatever the VoIP service you're using is assigned to . . . you can determine this under Voice services-->SP[freephoneline] Service-->X_CodecProfile),
4)ensure FAX Event is enabled, and
5)ensure under Codec Settings--> that FaxPassThroughCodec is set to G711U
6)T38Enable should be checked
(4, 5, and 6 should be default settings)
7) T38ECM is checked for me (and seems to work). This is not a default setting.
8. I would increase volume slightly:
Navigate to Physical Interfaces-->Phone Port-->
a) Change ChannelTxGain to -1
b) Change ChannelRxGain to 0
9) On your fax machine, lower baud rate to 9600 bps (I'm able to fax at faster rates than 9600, but if you can't without outgoing faxes failing, lower your baud rate to 9600)
10) On your fax machine, turn off or disable ECM (both TX and RX)
In your call status page, during T.38 protocol fax transmission, you'll see the following:
"Audio Codec = tx=; rx=G711U"
(which doesn't specifically state T.38, but this is the only indication OBi seems to provide)
If you're not using T.38, you'll see "Audio Codec = tx=G711U; rx=G711U" instead, which just means you're using the G.711u codec only.