Moving to Bulb from BG smart Paygo

I have a smart meter Pay as you Go with British Gas and just signed up to Bulb.
Anyone knows how this is processed. Obviously with BG i have to top up before using the energy and can see the balance coming down every day.
When i signed to Bulb it says the switchover day will be the 22nd October. So from that moment i would no longer make top up payments to BG, but would pay by direct debit to Bulb.
So what happens to the meter? Does it become credit meter on the day of switchover? I understand the display would stop working right?