Multi camera editing - different aspect ratios - layers

Hi, I have a vertical format video on top of a horizontal. I'm using the vertical as a kind of zoomed in view.

When I cut to the vertical camera, I get black edges.

How can I have the horizontal version show through underneath?

Here are a couple of screenshots.

This is how I want the finished item to look (and how I can see it in some views but not in the main view).

This is how it looks now.

This is shows the vertical video on top of the horizontal.

Thanks for looking, hope you can help. I'm something of a beginner with PP and not a pro editor.