Sends DTMF tones on the call. Each character in the string is transmitted as a separate tone in order, with timing managed by the server.
Accepted characters: digits 0–9, *, #, and the w / W wait separators (the lowercase w inserts a short pause, the uppercase W a longer one). Any other character produces an error from the server.
Requires the sendDigit capability — inspect call.capabilities$ before exposing a dialpad in your UI.
The digit string to send (e.g. '1234#', '1w234'). Each character is transmitted as a separate tone.
Promise<void> — resolves once the server has accepted the full string for playback.
capabilities$ to check whether digit-sending is permitted on this call.