Send Grid API in Node.js

Question

I am trying to get the contact list and check if the email recipient opened the email or not. I found this code and tried but got 401.

import config from "@server/config"
sgClient.setApiKey(config.sendgridKey)
  const headers = {
    "on-behalf-of": "my account user name"  // I put my account user name here
  }

  const request = {
    url: `/v3/subusers`,
    method: "GET"
  } as any
  const list = await sgClient
    .request(request)
    .then()
    .catch((err) => {
      console.log("list", err.response.body)
    })

What do I need to put for the header 'on-behalf-of'? What does the subuser's user name? And is there any example to get the 'email opened' event? I am using Node.js.

Thank you!