On the web, the sign in page is available by clicking the “Sign In” button at the top right of the page. In apps, it is accessed through the menu at the top left of the screen. If you continue to experience difficulty, most errors can be cleared by both closing all browser windows or hard-closing the app and then re-starting it.
To hard-close the app on an iOS device, press the Home button twice, then swipe upwards on the app to close it.
On Android, use the Android menu button on the bottom of the screen and swipe the app away to close it.
On Windows 8.1, press the device back arrow button on the bottom of the screen and swipe the app down to close it.