Are you using vscode-fhs? vscode-fhs is unable to deal with permission requests · Issue #350991 · NixOS/nixpkgs · GitHub
If you’re using vscode, you’d have to ensure you have a polkit agent set up. vscode uses pkexec to make that button work. Check the unit’s logs to make sure everything is working.
Testing on my end, the prompt shows up and works. But I don’t use a systemd service, I just start the agent via my sway config.