message: Set content-type header for joinSession request which has body
diff: @@ -72,6 +72,9 @@ export async function fetchJoinSession(
  if (guestDisplayName) {
  body.guestDisplayName = guestDisplayName;
  }
  + // IMPORTANT: Must set content-type header explicitly to application/json when request has body.
  + // By default, request will use text/plain as content-type and will be rejected by backend.
  + headers["Content-Type"] = "application/json";
  }
  const response = await runWithRetry(
  