Problem with extensions not being able to call each other

[Kamber KÜLAHCI]

Two internal numbers in our 3cx IP switchboard cannot call each other. We checked the settings of these extensions. There is no restriction or blocking. They are not on the blacklist either. However, when one number calls another number, it gives a warning saying 'The number you are calling is busy'. What should we do?

 

[TheodorosG_3CX]

Are you using ip phones or the Web Client?
Have you checked the extension status?