YouTube scheduled livestreams may not go live, (and will display an error message in newer versions of Ecamm Live) if the scheduled livestream is inadvertently created as a "Webcam" stream rather than a "Streaming Software" stream.
To prevent this from happening, schedule using Ecamm Live instead, or be sure to follow these steps when creating a stream using YouTube Studio:
In YouTube Studio, ensure that you are in the Manage section.
Click the blue SCHEDULE STREAM button to create a new stream.
3. Once scheduled, double-check that the Type is Streaming Software as shown in the image above.