Error 0x80EF0197

Value: -2131820137 | 0x80EF0197 | 2163147159

What does it mean ?

RTC_E_STATUS_CLIENT_PROXY_AUTHENTICATION_REQUIRED  
Proxy Authentication Required
Value: 407 | 0x0197 | 0b0000000110010111

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