Getting an error while getting in ringcentral extension.......You cannot use this device to make PSTN calls including Emergency Calls since no Digital Line is associated.

Tell me more about what you did. What environment, sandbox or production. And the exact steps that took you there.

The message said that you don't have a digital line associated with the user extension. Can you login the service web, select the user -> User Details -> Phone to see if the user has a device or not. If not, click the "Add Phone" button to add a digital line to that user extension and try again.