There is a line in your service.ashx file that looks like this:
Code:var hasCodeSessions = sessionManager.DoSessionsExist(InvitationType.Code);
In 2.3 it needs to be changed to look like this:
Code:var hasCodeSessions = sessionManager.GetSessionSummaries(InvitationType.Code).Any(ss => !ss.IsGuestConnected);
In 2.4 it needs to look like this:
Code:var hasCodeSessions = sessionManager.GetSessionSummaries(InvitationType.Code).Any(ss => ss.GuestConnectedCount == 0);