I do not have a 7D II (but I do have the 600EX-RT). Check your menus to make sure you didn't set the flash to 'disabled'. It is possible to use the flash as a remote commander (master) for slave flashes. Under the 'flash control' menu, you should see settings for the external flash. Make sure it isn't disabled.
It is ALSO possible to use the menu buttons on the flash itself to disable the flash (and that overrides the camera settings). I'd check that as well.
Yes, the button that lights up red and has the lightning bold symbol above it is the Test flash button. When it is red, pressing the button should fire a test flash. If the flash is not mounted to the camera does pressing the test button fire the flash head?
If the test flash button does not fire the flash head I recommend contacting our Technical Support team for assistance. They can be reached HERE or at the link below.
09/26/2023: New firmware updates are available.
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