Aftrer Effects wont display transparent background in web flow

Iv created a .mov quick time rgb alpha file in after effects that is supposed to have a transparent background in webflow however when I loads the file in Background Video the background displayed is black with the red square in the center. Is it possible to make a transparent background in webflow using quicktime .mov file in Background Video.

Webflow - Grafik Saphir

Here is my public share link: LINK
(how to access public share link)

I follow this tutorial and still it wont work.