Could you please try the following steps: 1. On primary machine, run spacedesk SERVER window, click the menu button then select "Clear All Display Settings". 2. on secondary machine / tablet, go to Settings -> Rotation -> Auto-Rotation, then uncheck it.
After the steps above, please try to connect again. FYI: Once connected, you can easily switch to extension/mirror via display settings window on your primary machine. For assistance, please refer to our spacedesk user manual on how to operate and troubleshoot Looking forward to your feedback.