Small contracting on side of a main gig

I love programming, and don't get enough of it at my FAANG day job. I've got my manager's permission to do a few small personal projects on the side which keep me engaged. Whether they make a small amount of money or not doesn't matter to him, as long as it's not a "competing field" as my employer and doesn't impact my day-to-day work. Now I have some opportunities for similar projects but for a fixed contract fee. I don't expect this to be seen nearly as favourably as my "personal projects", which I totally understand (even though the time investment is the same).

Before I ask my manager, has anyone succeeded at getting this kind of arrangement? Any tips?