Something not working?

SnapAudio has no Dock icon — it's a menu bar app. Look at the top-right of your screen for the speaker icon. Its settings window opens by itself the first time you launch it.

Two different things look the same here. If you turned the icon, the device name and the volume level all off in Settings → General, SnapAudio shows nothing in the menu bar — open it again from Applications and the settings window comes back on its own.

If the menu bar is just full, macOS drops whatever doesn't fit. A menu bar manager gets the room back: Hidden Bar, Ice, and Bartender all collapse the icons you never look at, and the first two are free. SnapAudio's own item can be narrowed as well — the device name, the volume percentage and the indicator are separate toggles in Settings → General.

Worth doing before it happens — give Open Settings a shortcut in Settings → Actions. It ships without one.

Another app has probably claimed the same combination — macOS gives it to whoever registered first, and SnapAudio only checks its own shortcuts for clashes. Try something on ⌃⌥: macOS itself claims one combination there, ⌃⌥Space.

The mute happens in the device itself, and some USB adapters and wireless headsets don't support it. When the current input doesn't, SnapAudio says so instead of failing silently.

Open Settings → Devices and drag the device you want to the top of the list. The order is the priority order — SnapAudio uses it to decide which device wins when something connects or disconnects.