It may occur that a user can not sign in. The following things need to be checked if this occurs.
1. Make sure that the device has a strong 3G, 4G or Wifi-connection.
2. Make sure the username and password are spelled correctly. Perhaps @ or .co.uk has been forgotten, the name might have been misspelled or the e-mail address and/or password do not start with a capital letter.
If signing in still does not work, click on Problems signing in? at the bottom of the screen. The password can then be reset by following the instructions in the screen.