Canon Speedlite 600EX II-RT Manual (en)

Troubleshooting Guide
Set the flash coverage to <L> (automatic) (p.38).
Insert the mounting foot into the camera’s hot shoe all the way, slide 
the lock lever to the right, and secure the Speedlite to the camera 
Remove the bounce adapter (p.36).
Retract the wide panel (p.39).
Set the camera’s shooting mode to <d/s/f/a/bulb(B)
(Creative Zone mode).
Set the Speedlite’s power switch to <K> instead of <a> 
The flash coverage is not set automatically.
The flash coverage cannot be set manually.
Functions cannot be set.