Error 0x80EF01F5

Value: -2131820043 | 0x80EF01F5 | 2163147253

What does it mean ?

RTC_E_STATUS_SERVER_NOT_IMPLEMENTED  
Not Implemented
Value: 501 | 0x01F5 | 0b0000000111110101

Where does it come from ?

FACILITY_SIP_STATUS_CODE  
SIP - Session Initiation Protocol (VoIP)
Value: 239 | 0x0EF | 0b11101111

Other Errors for FACILITY_SIP_STATUS_CODE