It seems a lot of writers use maybe in the place of “may be” a bit too often, maybe. The word maybe is an adverb (do you remember what those are? They modify a verb). It means perhaps. So anytime you can use perhaps in the spot you want to write maybe, you are A-OK.
So when are you not supposed to use maybe and use may be instead? Remember, may is a verb. You may go outside if I say so. You may do it anyway. You may be a bit belligerent. You may be tuning me out. But I’m used to it. Think “might be” or “could be.” Or maybe not.