google calendar apiで401エラー

前提・実現したいこと

https://developers.google.com/calendar/quickstart/js
googleカレンダーapiの公式を見ながらクイックスタートをやっているのですが、以下のようなコンソールをみると401エラーが帰って来ています。
googleカレンダーでIDとapi_keyはしっかり取得したはずです。
原因がわかる方がいましたらコメントお願いします。

発生している問題・エラーメッセージ

cb=gapi.loaded_0:151 Uncaught {result: {…}, body: "{↵ "error": {↵  "errors": [↵   {↵    "domain": "gl…e": 401,↵  "message": "Invalid Credentials"↵ }↵}↵", headers: {…}, status: 401, statusText: null}

該当のソースコード

<!DOCTYPE html>
<html>

<head>
  <title>Google Calendar API Quickstart</title>
  <meta charset="utf-8" />
</head>

<body>
  <p>Google Calendar API Quickstart</p>

  <!--Add buttons to initiate auth sequence and sign out-->
  <button id="authorize_button" style="display: none;">Authorize</button>
  <button id="signout_button" style="display: none;">Sign Out</button>

  <pre id="content" style="white-space: pre-wrap;"></pre>

  <script type="text/javascript">
    // Client ID and API key from the Developer Console
    var CLIENT_ID = 'hogehoge';
    var API_KEY = 'hogehoge';

    // Array of API discovery doc URLs for APIs used by the quickstart
    var DISCOVERY_DOCS = ["https://www.googleapis.com/discovery/v1/apis/calendar/v3/rest"];

    // Authorization scopes required by the API; multiple scopes can be
    // included, separated by spaces.
    var SCOPES = "https://www.googleapis.com/auth/calendar.readonly";

    var authorizeButton = document.getElementById('authorize_button');
    var signoutButton = document.getElementById('signout_button');

    /**
     *  On load, called to load the auth2 library and API client library.
     */
    function handleClientLoad() {
      gapi.load('client:auth2', initClient);
    }

    /**
     *  Initializes the API client library and sets up sign-in state
     *  listeners.
     */
    function initClient() {
      gapi.client.init({
        apiKey: API_KEY,
        clientId: CLIENT_ID,
        discoveryDocs: DISCOVERY_DOCS,
        scope: SCOPES
      }).then(function () {
        // Listen for sign-in state changes.
        gapi.auth2.getAuthInstance().isSignedIn.listen(updateSigninStatus);

        // Handle the initial sign-in state.
        updateSigninStatus(gapi.auth2.getAuthInstance().isSignedIn.get());
        authorizeButton.onclick = handleAuthClick;
        signoutButton.onclick = handleSignoutClick;
      }, function (error) {
        appendPre(JSON.stringify(error, null, 2));
      });
    }

    /**
     *  Called when the signed in status changes, to update the UI
     *  appropriately. After a sign-in, the API is called.
     */
    function updateSigninStatus(isSignedIn) {
      if (isSignedIn) {
        authorizeButton.style.display = 'none';
        signoutButton.style.display = 'block';
        listUpcomingEvents();
      } else {
        authorizeButton.style.display = 'block';
        signoutButton.style.display = 'none';
      }
    }

    /**
     *  Sign in the user upon button click.
     */
    function handleAuthClick(event) {
      gapi.auth2.getAuthInstance().signIn();
    }

    /**
     *  Sign out the user upon button click.
     */
    function handleSignoutClick(event) {
      gapi.auth2.getAuthInstance().signOut();
    }

    /**
     * Append a pre element to the body containing the given message
     * as its text node. Used to display the results of the API call.
     *
     * @param {string} message Text to be placed in pre element.
     */
    function appendPre(message) {
      var pre = document.getElementById('content');
      var textContent = document.createTextNode(message + '\n');
      pre.appendChild(textContent);
    }

    /**
     * Print the summary and start datetime/date of the next ten events in
     * the authorized user's calendar. If no events are found an
     * appropriate message is printed.
     */
    function listUpcomingEvents() {
      gapi.client.calendar.events.list({
        'calendarId': 'primary',
        'timeMin': (new Date()).toISOString(),
        'showDeleted': false,
        'singleEvents': true,
        'maxResults': 10,
        'orderBy': 'startTime'
      }).then(function (response) {
        var events = response.result.items;
        appendPre('Upcoming events:');

        if (events.length > 0) {
          for (i = 0; i < events.length; i++) {
            var event = events[i];
            var when = event.start.dateTime;
            if (!when) {
              when = event.start.date;
            }
            appendPre(event.summary + ' (' + when + ')')
          }
        } else {
          appendPre('No upcoming events found.');
        }
      });
    }



  </script>

  <script async defer src="https://apis.google.com/js/api.js" onload="this.onload=function(){};handleClientLoad()"
    onreadystatechange="if (this.readyState === 'complete') this.onload()">
    </script>
</body>

</html>