App crashes when clicking (STUCK?)

Answer 1

Do some troubleshooting:
Check your internet connection, swap from wifi to your phone's data, or the other way around - try another wifi, if possible.
Close all your apps and try the lesson again.
Clear your cache, try again.
Restart your phone, try again.
Reinstall the app, try again.
Should all else fail, send an email to [e-mail] with screenshots.