On the switch that has two cables in L1 and L2.
First of all, mark the conductors so you don’t mix them up.
The pair of wires that are in L1 goes to the LIVE terminal on the MASTER dimmer.
The other pair goes to LOAD on thd naster dimmer.
The black goes to the S terminal.
https://www.varilight.co.uk/leaflet...ro_Multi-Point_Remote_Dimmer_Instructions.pdf
On the slave dimmer, black goes to the S terminal.
The other two wires go to live and load.
If your dimmers have metal front plates then you must connect earth to the plate.
That should do it.