4452d530_able___FreeSWITCH___Confluence__Description
[ITU-T Q.850 Code] 6 [Enumeration] CHANNEL_UNACCEPTABLE [Cause] channel unacceptable [Q.850] [Description] 
This cause indicates that the channel most recently identified is not acceptable to the sending entity for use in this call.
Hangup Cause Code Table - FreeSWITCH - Confluence
Description