I checked that - Mini R4 also has 3.3V on S1 and S2
Check if your cables are connected correctly. Is there definitely voltage on L1?
If there is voltage on L1, it is the same on S1.
Terminals (L in) and S1 are connected.
That’s very unlikely since S1 and L are connected as ociepa.ekotox stated many times before. Therefore, on S1 should be line voltage if you connected wires correctly. L = live (line). Be safe when manipulating!