Zendesk Update Users API From Google Sheets

I'm going to start by saying it's immensely frustrating half knowing how to do something but never quite being able to finish; this is another one of those projects for me.

Scenario: Using a Google Sheet and Apps Script I am attempting to update several User records in Zendesk using their https://developer.zendesk.com/api-reference/ticketing/users/users/#update-many-users data-science

I think i probably have most if it right (i stand to be corrected of course) with the following script however I just cannot get it to update any records. I suspect it might be to do with how the array is presented (an area I sadly don't know enough about).

function updateManyUsers(){
var sheet = SpreadsheetApp.getActiveSpreadsheet().getSheetByName('Sheet1');
 var [headers, ...rows] = sheet.getDataRange().getValues();
 var data = {}
 var items = []
 rows.forEach(function(r) {
   var obj={}
   r.forEach(function (c, j) {
     obj[headers[j]] = c
   })
    var data = {}//moved
   data['users'] = obj // moved this inside your loop
   items.push(data) // pushed the object into the items array
 })
 
 Logger.log("Log JSON Stringify Items: " + JSON.stringify(items))
 
 items.forEach(function(i) {   // added this to loop over objects in items
 var url = 'https://itsupportdesk1611575857.zendesk.com/api/v2/users/update_many.json'; //https://developer.zendesk.com/api-reference/ticketing/users/users/#update-user
 var user = 'myemailaddresshere/token';
 var pwd = 'mytoken';
 var options = {
     'method' : 'PUT',
     'headers': {
       'Authorization': "Basic " + Utilities.base64Encode(user + ':' + pwd)
     },
     'payload' : JSON.stringify(i),
     'contentType': 'application/json',
     'muteHttpExceptions': true
 };
 UrlFetchApp.fetch(url, options);
 Logger.log(i)
 var response = UrlFetchApp.fetch(url, options);
   Logger.log(response);
   
})

} 

I've gone through as much as I can following the documentation, I know i had the end points incorrect and the method(?) too (set to Post instead of Push). I have gone through varying error messages that I have tried to act upon and this is my current one: 

This is an image of the data in my sheet 

Suplimental: In order to get better at this i would like to put myself on a learning path but am unsure what the path is; most of my automation work and scripting is done using Google Apps script so would people recommend a JavaScript course? I alter between that and Python not knowing what would suit me best to get a better understanding of this kind of issue.

Many thanks in advance.