Green screen turns black

Hi. I have been following this tutorial

https://www.linkedin.com/learning/video-green-screen-workflows/an-introduction-to-keying-in-after-effects?u=2330002

and as soon as i use the screen colour eyedropper to select my green screen in keylight everything turns black when it should show me immersed with my arctic stock background.

I know its somwthing simple but i tried googling it and nothing came up. My stock footage is below my green screen footage.

Please help quick. Thanks