The MatchId is passed from Matchmaking into the GSDK using the "sessionId" configuration variable but in order to retrieve the ticket details using GetMatch, you also need the QueueName. If using the same build for multiple queues (casual/ranked, 1v1/2v2), this becomes a problem.
Since you already have a "sessionCookie" configuration variable that is unused during matchmaking, this would be a great way to pass in the QueueName so that the server can use GetMatch to successfully retrieve the ticket information. This is vital for making sure players are placed on the team as assigned by the matchmaker.