Relayed multiplayer matches like you’re creating by calling createMatch from the client cannot have labels. They don’t have any server-side state at all aside from the server’s own internal routing and match wiring, which you cannot control.
If you want to set a label and use it to look up matches you should look at authoritative multiplayer matches instead. You say you want a client-side solution but there’s no reason authoritative matches can’t be created using some amount of client-specified data. Just pass this through to your authoritative match creation RPC function and thread it through match creation on the server.
(Also please don’t tag specific people when you open a thread. Ask your questions and give the right info, we always do our best to reply to everyone.)