Flash key not working on remote GXW4004 as analog line extender (with GWX4104)


Hi everyone!!
I have a customer that has extended analog extensions of a PBX with GXW4004/GWX4104 over a Wireless link.
I’ve followed the setup videos that are around there and everything worked just fine.
There are two issues reported however:
1.- When trying to transfer a call from the remote GXW4004, pressing the FLASH key does not work and comunication gets dropped. You should hear a dial tone after pressning the FLASH key to dial the new extension to transfer the call, but that is not happening. I wonder if this feature works with this kind of direct IP call setup.
2.- Customer apparently has a fax on one of these remote extension, and call gets connected but fax is not received…

What do you think? Any suggestion?
Thanks in advance for your feedback.