Possible causes for this issue:

• No network coverage
• IMEI number might be blocked at service provider’s end.
• Low signal
• Network outage

Troubleshooting:

• Turn off the device and remove SIM card, reinsert SIM card and reboot your phone after 2 to 3 minutes.
• Make sure that your SIM card is in good condition, no scratches and make sure you insert it correctly.
• While performing outgoing calls, make sure your Wi-Fi is turned off.
• You can try switching 3G/4G to 2G and switching back to 3G/4G by following below steps

Go to Settings > Select More > Mobile networks > Preferred network type Select 2G/3G.
 

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             Possible causes for this issue:

• Data might have been cached on your dialler app.

Troubleshooting:

• You can go to Settings > Apps > you can see three categories on top Downloaded, Running and All.
• You need to select All and select Dailer
• After selecting dailer, you can find Clear data and Clear Cache.
• You can press Clear data and Clear Cache, It comes up with pop up that says ‘’ Delete app data’’ you can select okay.
• You can go back to main screen and try making a phone call to check whether the error still persists.
• If the error still persists, try to restart your phone.
• Please contact Sonim Support if this issue still persists.

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