I'm a beginner in photography. My company owns a Canon 6D with a Yongnuo YN560 III speedlight. I fixed the speedlight perfectly with the Canon 6d hot shoe. Sometimes the speedlight works in some setting (e.g., shutter 30, f/4, Auto ISO), but if I repeat the same, it won't work.
I set same shutter speed as Canon 6D in speedlight.