Troubleshooting

That is the browser withholding permission, not Cast. Click the padlock or settings icon next to the address bar, allow the microphone for this site, and reload — the device picker on the Record page then lists everything the browser can see.

If the right mic is listed but silent, check the input meter while you speak: no movement means the operating system is pointing at a different device, or the mic is muted at the hardware level.

One thing to know: the device cannot be switched mid-take — pick the mic before you press record.