Server teleportation - Get instanceId?

So here is my issue, I'm creating a script that allows you to connect to specific game servers, apoc style. Right now I have that function to join a server using InstanceId

void TeleportToPlaceInstance (
    int placeId,
    string instanceId,
    Player player = nil,
    string spawnName = "",
    Variant teleportData,
    ScreenGui customLoadingScreen = nil
)

Thing is, I cannot find how to get a server's instanceId. ( the server list will be updated using datastore ) So, does anyone know how to get the InstanceId ?

Thanks for helping ;)