A bit of further info on how it works....
For lots of other cars, on the Ohme you would set a schedule, and say I want the car to be at 80% charge by 9am tomorrow (say).
When you plug in the car, the Ohme would talk to the car and see it currently has 42%, so figure out it needs to add 38% to reach the 80% target.
38% of your 64kWh battery capacity is 24.3kWh. The Ohme then sends to Octopus a message saying "Hey! We need 24.3kWh by 9am tomorrow".
Octopus then does its stuff and sends back a schedule to the Ohme telling it when it can start and stop the charging (it may be more than one period, and if you need a big charge some of it may be outside the 11:30-05:30 hours).
You wake up and the car is charged!
But because the Ohme cannot (yet) talk to MGs, you must do the first bit of the calculation for it.
So, with the MG rather than saying I want reach 80% by 9am, you must tell it I want to add 38% by 9am (actually, I'd round it up to 40% myself). You have already told the Ohme what car you have so it knows the battery capacity and can then follow the process above from that point.
I hope that helps.
[edited to use your 42% starting SoC]