Meter Reading in Kwh
It appears you can record your tariff in kwh and set Kwh as your preferred measurement, but the add reading menu only states m2. Either this kwh needs to be added as a meter reading option or if the value entered is whatever you set your preferred measurement to, then the reference to m2 in the add meter reading ui needs to be removed.
The choice of m3 or kWh is directed at your displayed graph.
The reason that the meter readings is only in m3 is because the gas meters read in m3 and not in kWh as the meter simply measures your "volume" of gas supplied.
So your ability to select m3 or kWh applies only to what is shown on your display.........0
Add more data>Data source and unit>Heating unit>m30