I got it working - 2 days later!
In Project Settings > Pluginns > UDP Messaging : I made sure I had ticked “Enabled by Default” in the UDP settings - and clicked the “Set as Default” so the setting remained.
Then, in a Begin Event, made a Live Link Present variable, and used the Apply to Client node to make sure my LiveLink presents were manually set. (which I’d previously made in the LiveLink panel)
I then built it as “Development” - not tried “Shipped” yet.
References I followed that seemed to waste a lot of time:
and
Although I didn’t need to do any of the - message or ALLOW_UDP_MESSAGING_SHIPPING=1 - BUT I did run these in the console a load of times, so perhaps they helped? I even tried adding ALLOW_UDP_MESSAGING_SHIPPING=1 to the project files (named.Target.cs), but this killed my project!
Hope that helps someone…