Nokia 105 4G Fails to Connect

To make sure it is not caused by something open in the background or similar issue, restart your device by holding the power button down. This should refresh the connection.

If the SIM Card is damaged, it will need to be replaced.

Check if connected to the internet. Open the settings app on your device and go into the network settings, check to see if you are connected to your correct network. Ensure your network provider supports VoLTE

Check in your device's settings for any software updates, reserve a full factory reset as a last resort.