Why do I get the error 'The Microsoft account service is unavailable' when trying to install the app on Windows Phone?

On Windows Phone, you may see this message when trying to install an app.

This error occurs if the date and time is set incorrectly on your device.

To resolve the problem:

  1. Open the Settings on your device
  2. Open date+time
  3. Switch off Set automatically
  4. Manually enter the correct date and time