How can I set a backdrop for the video. I have the button but it doesn’t let me load anyting.
In the video call, if you click on Settings > Virtual Background, you’ll be able to choose between one of the existing blur/background options, or you can upload your own background. 
If you’re experiencing an issue with that, please submit a support ticket so we can take a closer look at what’s happening: https://demiplane.zendesk.com/hc/en-us/requests/new