Phoenix Multiplus Power Assist not working, looking for troubleshooting tips

HI all,

The power assist function does not appear to work on my Phoenix Multiplus 12/3000/120, when this inverter is in use, it will not operate power assist with the 2.8kW onboard genset (Mase 3.5i), either the inverter would work or switch over to mains power from the genset, but I could not make the power assist feature work, to “add” the inverter power to the genset when running, although I believe this size/age of multiplus had the feature? (Images of serial no below)

I have tried to trouble shoot this, but with no luck and am looking for advice on how to further test what the fault may be, or a setting to change to make it functional?

Anyone with any ideas?
Many thanks