Player Prefab Provider
The Dynamic Spawner option requires logic to decide which prefab will be spawned for each player.
In the image above, the "PlayerPrefabProvider" is the object with a component PrefabProvider which has a method called "GetPlayer"..
To create a Dynamic Spawner provider you will need to create a script to provide a player prefab to be spawned, this script shall implement the interface IInformationProvider to return the player prefab to be spawned ( see Providers Scripts ).
You can also check the example script PrefabPlayerProvider in the examples folder. This script has a full implementation of how to provide player prefab to be spawned.