This article provides instructions on how to troubleshoot the 'Error when changing single app mode state' error when using the Proctor mobile application on the iPhone.
Unable to start the exam on mobile phone because of the 'Error when changing single app mode state' error.
The problem looks as shown in the screenshot below:
Assessment Mode is not allowed on your phone.
The Proctor must be allowed to start Assessment Mode in order to start the exam:
Close the Proctor app on your phone and then follow the exam link again.
When prompted to confirm app self-lock, click Yes
Note: You will be unable to use other apps on iPhone until Proctor ends Assessment Mode.
Allow screen recording by clicking on OK: