S1 Sub and S2 Beam, S2 app won't find the Sub

I haven’t found an answer to this one via the search so apologies if this has already been answered.

I see that the S1 Sub is compatible with the S2 app, but the Beam S2 is only compatible with the S2 app. So why can't I add my S1 Sub to my media room with the S2 Beam via the S2 app? Just doesn’t see the Sub which I have disconnected from a S1 room completely.

My media room is run on my S2 App. Every other room is via S1 and is working just fine.

Thanks