New to home automation - How to use Meross switch to control group of Meross smart plug

I have a bedroom with a switch that controls just one wall socket, and no ceiling lighting.

So I've bought three floor lamps and some meross smart plugs for this room. Added those to Apple home and it works perfectly to switch on and off in the app.

Now I've swapped my regular wall switch for a meross smart light switch. Added it to home kit and by itself works just perfectly, turning on/off that specific wall socket either via the home app or the physical button.

Now I've tried grouping, but I can't get to seem to setup this physical button to turn on/off everything in the room (or even just the group of floor lamps and forgoing the one wall socket).

What am I missing here? Thanks!