Green Screen Composition - Subject is transparent

Hello. I have an issue with composition… a basic set-up. it should be not very difficult, but I might be missing something. I am trying to bring a real subject into an Unreal Engine 5 world.

I made use of the documentation for Composition as well as several online resources. I am using Cam Link 4K to bring my Fujifilm XT-4 video into the world and it works fine. I use that media source as input for my media_plate. I also have a cinematic camera that is being used as a CG element.

The material for the composition itself has two nodes that have the same name as the media_plate and the cg element, with another Over node in between that connects to the final Emission Color node (which is of Post Processing type). I also use a Keyer to get rid of the background.

The problem is that everything is transparent… If I put a mannequin in front of a wall and get rid of the color of the wall, the mannequin is see through… while the unreal engine 5 scene is seen properly. What am I missing? Timeline issues, project setup…? If you need I can attach images. Thank you.

For your CG renders to have the proper opacity for compositing, you will need to set Enable alpha channel support in post processing to Linear color space only enable in project settings:UE docs