Drambo (iOS)

I’ve just bought Drambo and installed on my M1 Mac Mini but I can’t get any sound and the sequencer won’t play. Anyone have any idea what I might be doing wrong? Whether or not the play button at the top is enabled the sequencer isn’t stepping through and I get no sound of any kind if I click any pads etc.

I have one other iPad app installed (ElasticDrums) and it works fine.

Absolutely baffled!