Google Apps Script for accessing NeverBounce RESTful API (and writing to a GSheet)

GASNeverBounce.gs

var VALID_COLUMN_INDEX = 4
var EMAIL_COLUMN_INDEX = 3

function onOpen() {
  SpreadsheetApp
    .getUi()
    .createMenu('Validate Emails')
    .addItem('Validate Sheet', 'validateEmail')
    .addToUi()
}

function validateEmail() {

  var properties = PropertiesService.getScriptProperties().getProperties()
  
  var API_SECRET = properties['API_SECRET']
  
  if (typeof API_SECRET === 'undefined') {
    throw new Error('You need to define a script property for the API Secret')
  } 

  var API_USERNAME = properties['API_SECRET']

  if (typeof API_USERNAME === 'undefined') {
    throw new Error('You need to define a script property for the API Username')
  } 
  
  var headers = {
    "Authorization": "Basic " + Utilities.base64Encode(API_USERNAME + ":" + API_SECRET)
  }
  
  var payload = {
    "grant_type": "client_credentials",
    "scope": "basic user web",
  }
  
  var options = {
    "headers": headers,
    "method": "post",
    "payload": payload,
  }
  
  var json = UrlFetchApp
  .fetch('https://api.neverbounce.com/v3/access_token', options)
  .getContentText()
  
  var accessToken = JSON.parse(json).access_token

  var dataRange = SpreadsheetApp
    .getActiveSpreadsheet()
    .getSheetByName('Sheet1')
    .getDataRange()

  var data = dataRange.getValues()
  var header = data.shift()

  data.forEach(function(row) {
 
    payload = {
      "access_token": accessToken,
      "email": row[EMAIL_COLUMN_INDEX],
    }
    
    options = {
      "method": "post",
      "payload": payload,
    }
   
    var json = UrlFetchApp
      .fetch('https://api.neverbounce.com/v3/single', options)
      .getContentText()
      
    var response = JSON.parse(json)  
    var success = response.success
    row[VALID_COLUMN_INDEX] = (success) ? response.result : response.msg
    
  })

  data.unshift(header)
  dataRange.setValues(data)
  return  
}