hasura-actions-examples signup "message": "the key 'message' was not present

const fetch = require("node-fetch");
const bcrypt = require("bcryptjs");
const jwt = require("jsonwebtoken");

const HASURA_OPERATION = `
mutation ($username: String!, $password: String!) {
  insert_user_one(object: {
    username: $username,
    password: $password,
  }) {
    id
  }
}
`;

// execute the parent mutation in Hasura
const execute = async (variables, reqHeaders) => {
  const fetchResponse = await fetch("http://localhost:8080/v1/graphql", {
    method: "POST",
    headers: reqHeaders || {},
    body: JSON.stringify({
      query: HASURA_OPERATION,
      variables,
    }),
  });
  return await fetchResponse.json();
};

// Request Handler
const handler = async (req, res) => {
  // get request input
  const { username, password } = req.body.input;

  // run some business logic
  const salt = bcrypt.genSaltSync();
  let hashedPassword = await bcrypt.hash(password, salt);

  // execute the Hasura operation
  const { data, errors } = await execute(
    { username, password: hashedPassword },
    req.headers
  );

  // if Hasura operation errors, then throw error
  if (errors) {
    return res.status(400).json({
      message: errors.message,
    });
  }

  const tokenContents = {
    sub: data.insert_user_one.id.toString(),
    name: username,
    iat: Date.now() / 1000,
    "https://hasura.io/jwt/claims": {
      "x-hasura-allowed-roles": ["user", "anonymous"],
      "x-hasura-user-id": data.insert_user_one.id.toString(),
      "x-hasura-default-role": "user",
      "x-hasura-role": "user",
    },
    exp: Math.floor(Date.now() / 1000) + 24 * 60 * 60,
  };

  const token = jwt.sign(tokenContents, process.env.AUTH_PUBLIC_KEY);

  // success
  return res.json({
    ...data.insert_user_one,
    token: token,
  });
};

module.exports = handler;