You probably have inadvertently set something that is causing the problem.
Do a Factory Reset!
All I can find on the Internet is the Basic Manual.
I don't find what I was looking for in that Manual.
If you have the complete Manual look for a Menu setting that will let you reset the camera to factory settings.
Most camera manuals have it on the setup Menu.
..
Hi! I just got a Panasonic Lumix GX7 yesterday. I did a few indoor test shots and the little built-in flash worked fine. However, today I cannot get it to work. It will pop up but won't fire and also on the set-up menu, "flash" is grayed out. I cannot even select "flash" to look at the settings. The manual has been no help.

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