Gluster users - Nov 2021 - mixing peers from ver 8 & 9

Hi guys.

I'm trying to add a peer of ver 9 to cluster running of ver 
8 and I get "infamous" - Peer Rejected (Connected)
I do not see why that would be other than versions 8 & 9 
being 'incompatible'.
Has anybody tried such a mix?
many thanks, L>