How can I use FaceTime Audio with MacBook in clamshell / lid closed? At my desk I use my 11" MacBook Air with the lid closed, an external monitor with no camera, and a headset with microphone. I have just updated to Mojave from Sierra, and can no longer use FaceTime Audio in that configuration. I'm looking for a way to stop FaceTime from waiting for video from the inactive FaceTime camera.

Under Sierra, I could open the FaceTime app, and place or receive FaceTime Audio calls normally. 

Now, under Mojave, when I open FaceTime, the window is black, and after a minute or so, I get an alert saying "No Video - FaceTime has not received any video from the connected camera. Restarting the computer may fix this issue." I'm not able to place calls, and restarting doesn't help. It's not clear whether I can receive calls or not.

I can plug in an old USB webcam, but I'd rather not as it seems to use a significant amount of CPU, and also my USB ports are currently all in use.

Is there a software solution I can use to make this work without having to  keep the lid open or plug in a camera? Is there some hidden preference to tell FaceTime to ignore the camera, or could I create a "dummy" camera interface or something like that? Would updating to Catalina solve the problem?
Here's a solution which works for macOS >= 10.14. One can initiate a call in Messages by clicking on details in a chat history and then on the phone symbol.

https://support.apple.com/en-gb/guide/messages/icht1091/mac