Note: If you have signed up for your account after 24 April 2023, please visit the following article: Adding or Recharging Your Phone Credits
If the agent is online and microphone access is also enabled but the agent is not able to receive any calls, it could be that the agent has not been added to the appropriate team.
To view if the agent is added to the team:
Go to Admin Settings > Users and Permissions > Phone Teams.
Click on the edit button next to the team name and add or remove agents. For details, see How to add phone teams?