We had a great impromptu conversation one night about proper grip, pronation, supination, and wrist involvement in proper badminton strokes.
Here’s a video that explains the typical wrist movement in a stroke. The part where he gets into gear ratios with his chalk board can be a bit much, but you can try to follow along.
The key thing here is that your wrist goes into the extension position (cocking back the racquet) and to neutral for the pronation/supination and follow through of a stroke. There is no flexion.
It is not to say that flexion does not play a role – because it does. But first we must understand how power is generated through pronation and supination, and to master that concept before moving on!