First Run

Shared Clipboard needs two things the operating system guards: permission to reach other devices on the local network, and permission to run at all as an application from outside the app store.

Both prompts appear once.

macOS

Gatekeeper. The first launch is refused because the build is not signed with an Apple Developer certificate. Right-click the application and choose Open, then confirm. The plain double-click will work from then on.

Local Network. macOS asks whether the application may find devices on your network. This is the permission the whole feature rests on.

If you decline the local network prompt, the application still starts and looks like it is working — it simply never discovers anything. Re-enable it under System Settings → Privacy & Security → Local Network.

Windows

SmartScreen. A blue "Windows protected your PC" panel appears for the same reason as Gatekeeper: the build is unsigned. Choose More info, then Run anyway.

Defender Firewall. Windows asks which networks the application may communicate on. Tick Private networks. Leave public networks unticked — this application is not meant for them, as Security explains.

Linux

No prompts, but the clipboard tooling has to be present. See Installation for the package list.

Checking that it worked

Start the application on two machines on the same network, copy some text on one and paste on the other. If nothing arrives, Troubleshooting starts with discovery.