My mother in law purchased this home plan with the understanding that the modem could be connected to an external antenna.
During the setup I discovered that the device requires a setting to be changed in the mobile broadband settings to change it from internal to external antenna.
I discovered that when creating the firmware and default profile for TPG they did not define the APN information which causes error 89527, meaning that you cannot change the setting to utilise the external antenna.
Furthermore if you change to another profile which can change to the external antenna you are unable to return back to the TPG profile because of the same error. The only way to get back onto the internet is to factory reset the modem.
TPG support explained to me that they cannot assist to create a new profile, and will not attempt to fix the issue with the default profile but instead advise to only use the internal antenna.
This is not an adequate solution, we installed an antenna on the roof because that is the only way to get a reliable signal.
With no bin file to backup/restore and no ability to ssh, I believe that the only solution is for TPG to provide a firmware update to correct the APN error.