Cannot GET /slack/receive?code=xxx.yyy.zzz&state=botkit

CLIENT_ID=xxxx CLIENT_SECRET=yyyy VERIFICATION_TOKEN=zzzz PORT=443 npm start

...
** Configuring app as a Slack App!
events.js:141
      throw er; // Unhandled 'error' event
      ^

Error: listen EADDRINUSE :::443
    at Object.exports._errnoException (util.js:870:11)
    at exports._exceptionWithHostPort (util.js:893:20)
    at Server._listen2 (net.js:1237:14)
    at listen (net.js:1273:10)
    at Server.listen (net.js:1369:5)
    at EventEmitter.listen (/var/www/html/node_modules/express/lib/application.js:617:24)
    at Object.Slackbot.slack_botkit.setupWebserver (/var/www/html/node_modules/botkit/lib/SlackBot.js:179:41)
    at Object.<anonymous> (/var/www/html/index.js:60:12)
    at Module._compile (module.js:410:26)
    at Object.Module._extensions..js (module.js:417:10)
    at Module.load (module.js:344:32)
    at Function.Module._load (module.js:301:12)
    at Function.Module.runMain (module.js:442:10)
    at startup (node.js:136:18)
    at node.js:966:3

npm ERR! Linux 4.4.0-57-generic
npm ERR! argv "/usr/bin/nodejs" "/usr/bin/npm" "start"
npm ERR! node v4.2.6
npm ERR! npm  v3.5.2
npm ERR! code ELIFECYCLE
npm ERR! [email protected] start: `node index.js`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the [email protected] start script 'node index.js'.
npm ERR! Make sure you have the latest version of node.js and npm installed.
npm ERR! If you do, this is most likely a problem with the workbot package,
npm ERR! not with npm itself.
npm ERR! Tell the author that this fails on your system:
npm ERR!     node index.js
npm ERR! You can get information on how to open an issue for this project with:
npm ERR!     npm bugs workbot
npm ERR! Or if that isn't available, you can get their info via:
npm ERR!     npm owner ls workbot
npm ERR! There is likely additional logging output above.

npm ERR! Please include the following file with any support request:
npm ERR!     /var/www/html/npm-debug.log