Fax documents can only be sent internally and to other areas that differ from your local prefix. If a fax is to be sent externally to the same public line access, this is not possible. An alternative outside line access code is used instead of 0 for outside line access.
Open the XPhone server's web admin interface and edit the 'LocalAccess' parameter under UM -> GATEWAY in ADVANCED SETTINGS. Enter the outside line access configured for XCAPI in the PBX system. If the 'LocalAccess' parameter does not yet exist, create a new one.