It‘s not that easy, unfortunately.
We used a dedicated channel where referees post game dates, and when people say they want to play on that day, the announcement is updated to include their name. If not enough people sign up, the game is cancelled.
There is a social channel that provides community and prevents the server from falling away into ignored-land. Not sure how important that is.
We keep signing up and chat about the game in a separate channel so that the “next games” channel sticks out.
If the pool of players is small, offer a role to people interested and tag it in the announcements.
That‘s all I got.
Going from “referee proposes a date and players sign up” to “players ask me for available dates and recruit fellow players to the expedition” took me 45 sessions…
#RPG