Onion skin not working on bitmap layers?

I am relatively new to Toon Boom but pretty much know how to use it now, only onion skin is not showing up on bitmap layers! I definitely have it turned on and it works fine on vector layers, but on bitmap the onion skin will not show. I have tried restarting the program and my computer but I’ve been having this issue for days now, what can I do?

Onion skinning only works with vector images or transparent bitmaps.
If your bitmaps are opaque you will only see a pink box if the position of
the bitmap changes over time.

If you’re working with bitmaps it will be better to change the Onion Skin
Render Style on the Drawing tab of the preferences to “Normal” instead
of “Enable Shade”