Most signal errors have something to do with your SIM card or network coverage.
Make sure the SIM Card is inserted correctly.
If you're connected, while 2G and 3G networks are usually available, LTE connectivity can often be weaker depending on your area. Make sure that your SIM card's contacts are clean, and if you're using an adapter, it must not move around once placed on the SIM tray.
Confirm APN settings with your network provider to avoid no network/low network issues."
If the issue is not resolved, please contact firstname.lastname@example.org for further help.