Making a mask to keep pupils inside eyes

I’ve looked at some tutorials regarding making masks in Animate, but am having trouble getting down the process of creating a mask around a character’s eyes that will keep the pupils from appearing outside of them, like real pupils. I’ve created a mask layer that takes up the same spot as the eyes, but attempts to put the mask and pupils together always results in the pupils becoming invisible. What’s the correct way to go about this? I’ve included a screen capture of my character.

Which ones have you looked at?

I will see if I have any others.

Are there any good masking tutorials for something like this online? I know how to add a mask layer, but not which layer/s I should move to within it, like the pupils or the actual eyes.