By “casting” it means it is trying to turn the input value to an object, and it errored trying to do so.
You don’t need to iterate over the PassengerTable to teleport them all to the same server. TeleportToPrivateServer's 3rd argument accepts an array of players.
TeleportService:TeleportToPrivateServer(7936258099, reservedServer, PassengerTable, passengers.Value)
