Ubiquiti deprecated the Java tool. Download the from their community site or use:
For users who require this specific version, several workarounds have been identified by the community: ubnt discovery tool v251 and java on windows 10 updated
Because maintaining legacy Java installations on Windows 10 presents a security risk, Ubiquiti has shifted focus. The most "updated" way to use Discovery functionality on Windows 10 without Java headaches is the . Ubiquiti deprecated the Java tool
Ubiquiti has largely replaced the Java Discovery Tool with: ubnt discovery tool v251 and java on windows 10 updated
If you have a newer Java version installed, you may need to uninstall it and specifically install version 8u251 to get the .jar file to open correctly. Quick Setup Steps