One common cause for calls that show 'Forbidden' is related to  ‘Spoofing’: if you are trying to spoof a number and/or you think it may be possible that you are attempting to present a caller line ID / outbound number other than the main trunk number, first refer to I Can’t Get Spoofing to Work and I Can Get The Trunk Registered But I Can’t Make Calls.

There are other reasons why a call may be forbidden, or barred and there is a 'Barred Calls Log' function with the 'Logs' tab.

The 'Barred Calls Log' expands upon the CDR 'Hangup Cause' by giving a detailed reason for a call that has been barred and is an excellent first for to call for troubleshooting.  For a list of error codes / reasons please refer to Barred Calls Error Codes.