I followed the steps in https://developers.ringcentral.com/guide/notifications/webhooks/quick-start to create webhook-notification.js but when I run the resulting file, it fails with MODULE_FOUND

~/ringcentral $ node ./webhook-notification.js 

internal/modules/cjs/loader.js:888

  throw err;

  ^



Error: Cannot find module '@ringcentral/sdk'

Require stack:

- /home/x/ringcentral/webhook-notification.js

    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:885:15)

    at Function.Module._load (internal/modules/cjs/loader.js:730:27)

    at Module.require (internal/modules/cjs/loader.js:957:19)

    at require (internal/modules/cjs/helpers.js:88:18)

    at Object.<anonymous> (/home/x/ringcentral/webhook-notification.js:2:21)

    at Module._compile (internal/modules/cjs/loader.js:1068:30)

    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1097:10)

    at Module.load (internal/modules/cjs/loader.js:933:32)

    at Function.Module._load (internal/modules/cjs/loader.js:774:14)

    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:72:12) {

  code: 'MODULE_NOT_FOUND',

  requireStack: [ '/home/x/ringcentral/webhook-notification.js' ]

}

I'm new to node.js so if there is a trivial error in the example code, I might have missed it.