Cinema 4D Greenscreenfootage with Alphachannel is not Transparent


Hi Everyone!

I wanted to put a Person into an airplane Cockpit using Greenscreen and a simple Plane.
The Greenscreenfootage is already keyed with after effects, so it was not necessary to do inside Cinema4D.

The Issue: as you can See, the Plane itself with the Greenscreenfootage on it, is not fully Transparent. In order to understand it better here’s a picture of what it looks like:

When i look at the viewport, everything seems fine. But as soon as i prerender the image, or render it out, the plane gets visible. First i thought it has something to do with fog, but it doesn’t help.
Some important settings i use in the setup:
-Physical sky with fog - fog is around 5%
-Global Illumination with HDRI
-Ambient Occlusion
-Motion Blur on the Plane