Don’t think the id works like that. What you could do is reserve it and when they join they enter the main game and immediately redirect them to the reserved server
I don’t think reserved servers can have links, thats just private servers manually made. What I suggested is the only thing I can think of.
Send the person a link of the main game and as they joining check a data store or memory store to see if they’ve been invited somewhere and if so try to seamlessly send them to the reserved server.
The flaw here is if the player has been invited but doesn’t want to go to the reserved server and instead wants to go to the main game.
The the best case is just to store invites in a memory or data store and send pop up invitation requests when they join the main game.