I'm having a strange issue with my Canon camera. The first time I pop up the built-in flash after turning it on, it makes rapid shutter/clicking sounds and then displays Err 20. If I turn the camera off and back on while leaving the flash popped up, it works normally and I can take photos with no problem.

Has anyone experienced this before or know what might be causing it?

Video is attached for reference. Any help would be greatly appreciated.