The code property of the OTPCredential interface contains the one-time password (OTP).

A string containing the OTP.

The below code triggers the browser's permission flow when an SMS message arrives. If permission is granted, then the promise resolves with an OTPCredential object. The contained code value is then set as the value of an <input> form element, which is then submitted.

navigator.credentials
  .get({
    otp: { transport: ["sms"] },
    signal: ac.signal,
  })
  .then((otp) => {
    input.value = otp.code;
    if (form) form.submit();
  })
  .catch((err) => {
    console.error(err);
  });