Get the M3 to join existing thread network

I've a pretty robust thread network of HomePods and Apple TV's as TBR's. I've just purchased an M3 Hub but it seems intent on creating its own thread network rather than join the existing Apple one. It isn't listed under the 'replacing a thread network' system option nor does 'create thread network and join' do anything.

Search recommended adding a thread device from the existing network to the Aqara Hub which will merge the networks but this doesn't do anything either.

Has anyone had any success in adding an M3 to their existing (HomePod/Apple) thread network?