Yes, there’s another required step: I must enter the correct connection informations before the checkbox shows up.
The JS code checks for the connection, talks to the remote plugin and if it finds it’s all ok, lets the checkbox display itself. In other cases it hides the checkbox.
Now I believe this plugin has a weird design, because implementing in JS (client side) a server-to-server migration is at least a strange choice, but that’s another pair of shoes.