Multiple Parameter Banks in live.banks

Hi, complete beginner here so excuse me if this is a simple fix!

I've been editing a M4L device to add the live.banks object and use ableton device control for the 16 buttons on the M4L device.

I've managed to create one bank and map the first 8 buttons and it works just fine but I can't seem to add another bank to map the next 8 buttons. The "+" and "-" buttons bottom left don't add or remove banks.