Adobe Animate - Onion Skin doesn't show previous

Hi!

I'm trying to solve this problem for a while:

When I activate onion skin, I can't see the previous frame, I can see just the present frame even if I put the correct settings. I'm sure I'm using onion skin correctly because I watched a lot of tutorials to be sure I was doing it well.

I just can't see the previous frame, I've tried a lot of solutions but... Nothing.

Can you help me please? I can't animate without onion skin 😞