If you have a TRX system, then I assume that you were supplied with a MIDI Set Up file (.MSU) which should set the MIDI transmit and receive parameters correctly.
If you have somehow selected a different MIDI template (via a System Reset for example), this will remain as the selected template, and may be the cause of your problem.
User MIDI templates are saved to the USER drive, and so the TRX one may still be there.
To check, press Function > MIDI.
The display should open showing the MIDI template currently in use, highlighted. Note down the name and drive of the highlighted template. Is it on the PRESET or USER drive? If it is on the PRESET drive then it is one of the preset templates, and is unlikely to be the template for use with the TRX setup.
If necessary Tab to the USER drive and check the names to see if any of the listed templates here might be the TRX one.
If you see a template on the USER drive that has a different name to one of those on the PRESET drive, then this must be a User template and could be the TRX one, unless you have added your own User MIDI templates.
Try selecting the possible template and see if this restores the TRX functionality.
If this doesn't work you can select the same template that was in use when you started the check to return the system to the state that it was in at that time.