How to enable cross-buy?

Marble Mechanics (UE based) runs both as PCVR (Rift)  and stand-alone (Quest). Both are accepted and listed on their respective Meta Store. They share an App Group.

Is that sufficient to cause cross-buy to be active (i.e. one buys Quest then Rift is free or vice versa)? Is there some other switch/place that needs to be turned on? Documentation link would be fine too.