On some devices, the flash may not turn on during the scan. This is a known issue where another app running in background is using the camera and preventing the flash from turning on.
Affected devices:
If you have one of the following devices you may be affected by this issue.
Samsung A12, A13, A15, A16, A22.
Fix #1:
Restart the phone.
Fix #2:
Close the other apps that use the camera (social media apps, camera…).