Zap Desktop only support connection over the local network.
Where do I find my connection details?
Open the Lightning Node app on your Umbrel, open the three-dot menu and click Connect wallet. Choose Rest (Tor) from the dropdown menu.
Open Zap Desktop and click Connect on the welcome screen.
In the Connection String, enter <lndconnect URL>.
Click Next two times to confirm.
Congratulations! You have successfully connected Zap Desktop to your Umbrel.