4452d530_able___FreeSWITCH___Confluence__Description
[ITU-T Q.850 Code] 50 [Enumeration] FACILITY_NOT_SUBSCRIBED [Cause] requested facility not subscribed [Q.850 [Description] 
This cause indicates that the user has requested a supplementary service, which is available, but the user is not authorized to use.
Hangup Cause Code Table - FreeSWITCH - Confluence
Description