Let's say I have 3 sites (A, B, C). Only site B needs to be enabled on mobile devices. How do I achieve it?
I am aware of the isNativePhone and isNativeTablet functions, however, that is needed to be added in all the interfaces.
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In general the approach to enabling / disabling sites is conceptually based on user permissions. That is, if a particular user has access to site B, then they will expect to have access to site B whether they're viewing on a web browser or on mobile. If you have any particular user group that would only be using mobile, then you could potentially set up behavior similar to what you describe, otherwise I don't believe it's directly possible.