It is important for "Data Roaming" to be enabled when using a Huawei MiFi device.
The easiest way to do this is using the menu on the device itself:
1.) Power on the device.
2.) Once the device has started up, press the MENU button on the top seven times until the DATA ROAMING option is highlighted.
3.) Press the POWER button on the front of the device until a tick is now displayed in the box. Data roaming is now enabled.
You may see this while completing the above WiFi Extender Mode. Enabling this mode stops the 3/4G connection, so keep this disabled. If you struggle to get online, check it hasn’t been enabled by accident. It doesn’t really extend a WiFi source since there is no external antenna connection for WiFi.