Help video isn't visible when added as resource

[Eventastic]

Hai everyone, I realy hope you can help me. This sunday I'm hosting an online event for charity by a livestream on youtube live. So working on the livestream I wanted to add a mediasource > video. But when I add it, it is visible under sources, but it doesn't show the video in preview mode or when I click on transition. Can someone please help me?

Kind regards