Error

Error #0342: user UIN XXX is already in the conference UID YYY
 

Error description

A user with specified identifier (UIN) is already in the conference. For example, you try to invite them to a conference again.

 
Problem solution

As a rule, such an error can't happen as a client application controls the process of user invitation to other conferences.But if you work with MyChat directly by using an official open protocol, or write a script and send a command externally via Integration API, then make sure that you specify data correctly in the command you use.