If your system clock is 2 hours or more different from your valid local time, you will be prompted with the Error Code: 20 message.
You will need to have your parents or teacher refer to your device provider for proper instruction on how to update this to avoid further errors and interruption of your game. Links to some of their documentation can be found below.
Windows: How to set your time and time zone
Apple: Set the date and time on your Mac
Apple: If you can't change the time or time zone on your iPhone, iPad or iPod touch
Android: Set time, date & time zone