Typically, this is due to a cellular data restriction in the Settings menu of your smarthpone/tablet.
On Android device, use the steps below:
1. Select Settings.
2. Select Data Usage.
3. Scroll the list and choose Massagebook.
4. Select App Settings.
5. If the Restrict app background data option is toggled on, please toggle it off.
6. Restart the phone.
On an iPhone/iPad, use the steps below:
1. Select Settings.
2. Select Cellular.
3. Scroll the list and find Massagebook.
4. Toggle the button to the On (green) position.
5. Restart the iPhone/iPad.
Alternatively,
1. Select Settings.
2. Select scroll down and select Massagebook.
3. Toggle the Cellular Data option to the On position (green).
4. Restart the iPhone/iPad.