World I upload gets deleted when I start server?

So I am trying to set up a server with the Cero map (basically uno in Minecraft) and when I start up the server and join it, the map is not there. It just spawns me in a regular world. Any help on this? Also, I am using a Vanilla server (because the map maker says spigot breaks it) on 1.15.2. Also, this has happened to me before with pretty much any world.