Extension is not working

Hi, I am new to this. So I need a bit of help. I have an extension setup in the .ael file.The phone also seems to register correctly to the SIP account. But when I dial from outside or locally from another extension it is saying “extension at xxx is not available”. Can anyone please guide me to the right direction. Thanks in advance.

The exact configuration of the extension and your dialplan would be handy to help you debugging…