Expander 3.0 can only work with OpenSprinkler 3.0. If you have OpenSprinkler 2.x or OpenSprinkler Pi, you need Expander 2.1. You are right that the connectors have changed to avoid accidentally plugging in the wrong expander to the main controller. But it’s more than just a connector change: expander 2.1 and 3.0 work completely differently and so are not compatible at all. If you haven’t done so, you can send a support ticket to arrnage for an exchange.