4452d530_able___FreeSWITCH___Confluence__Description
[ITU-T Q.850 Code] 58 [SIP Equiv.] 503 [Enumeration] BEARERCAPABILITY_NOTAVAIL [Cause] bearer capability not presently available [Q.850] [Description] 
This cause indicates that the user has requested a bearer capability which is implemented by the equipment which generated this cause but which is not available at this time.
Hangup Cause Code Table - FreeSWITCH - Confluence
Description