Is there any particular trick to displaying the custom channels on GNX120 instruments via Actisense NGT-1?

In the dialogue box obtained via the menu (Instruments / com port / Actisense / Custom) I have chosen the custom channels to send out, ticked damping and given appropriate tag names.  I kept the Boat ID column as 0.

But yet on the instruments the display shows only dashes and the names custom 1, 2 etc.

I am using Expedition 10.14.5, latest Actisense NGT-1 firmware 2.690 and GNX120 has latest version 2.8.  The Actisense otherwise works OK and successfully connects the Garmin system to Expedition. 

is there anything else I need to have done in order to display Expedition data?

Thanks in advance for any insight