480 Temporarily Unavailable

[kelliejones001]

We are running OXO connect and OMC version 30.0.27.1
We have a couple of remote offices using the Telstra TIPT system.
Whenever we receive a call and try and to do a blind transfer to our remote office, the line drops with error from Alcatel "480 Temporarily Unavailable"

We don't have any firewalls between us and Telstra.
We can call the remote offices directly without issues.
If we do a warm transfer the call connects but they experience one-way audio.
We set up a test environment next to Alcatel and experienced no issues. Both phones were on the same LAN, but the traffic still goes out to Telstra.
We forced Telstra handsets and Alcatel to use G711 but this made no difference.

Any ideas on what the issue is would be greatly appreciated. Thanks.