Error 0x80EE0081

Value: -2131885951 | 0x80EE0081 | 2163081345

What does it mean ?

RTC_E_SIP_PEER_PARTICIPANT_IN_MULTIPARTY_SESSION  
A peer participant cannot be added to a multiparty session
Value: 129 | 0x0081 | 0b0000000010000001

Where does it come from ?

FACILITY_RTC_INTERFACE  
RTC - Real-time Communications
Value: 238 | 0x0EE | 0b11101110

StackOverflow

Other Errors for FACILITY_RTC_INTERFACE