Sharing Audio and video on a webinar

We created a webinar and we wanted to see if we could share video and audio at the same time (we figured it would be easy since we've been doing the same with our zoom meetings) 

During the practice session we tried to share video but the option to share audio is not clickable. The only other option was to share computer sound (which was not what we wanted). When we would play the video, there's no audio being heard by the panelists or anyone else in the room.