Usermeta update with AJAX

Hi everyone!

I created a costum page that, given the link of a csv file uploaded to the media, updates me a meta data of the users. I used jquery (ajax) and php.
I thought of inserting the ajax post call within the loop of the csv lines to progressively update the metadata per user. I do not think it is the correct way to proceed, however, because the console gives me error 502 and 429. What am I doing wrong?
Previously I had managed the loading of the csv and the update of the users only through php but with a large number of users it becomes a very heavy operation and gives me a 502 error. I was looking for a less cumbersome solution

Jquery

Query(document).ready(function( $ ){

 $( "#test-click" ).click(function() {
  
    $.ajax({
        type: "GET",
        url: 'FILE-CSV.csv',
        dataType: "text",
        success: function(data) {processData(data);}
     });

 
function processData(allText) {
    var allTextLines = allText.split(/\r\n|\n/);
    var headers = allTextLines[0].split(';');
    //var lines = [];

    for (var i=1; i<allTextLines.length; i++) {
        var data = allTextLines[i].split(';');
        if (data.length == headers.length) {

            var tarr = [];
            for (var j=0; j<headers.length; j++) {
                //tarr.push(headers[j]+":"+data[j]); 
              tarr[headers[j]] = data[j];
              //console.log(tarr['n']);
      $.ajax({
            url:"/wp-json/bluenext/updatelesson",
            method: "POST",
            //data: post_id,
            data: {id : tarr['id'], id_lezione : tarr['id_lezione']},
            success: function(response){
            
           console.log(response);

                }
            }) 
            }
            //lines.push(tarr);
        }
    }
     //console.log(lines);
}
  
  });
});

PHP

function updatelesson(){
  $user_id = json_decode($_POST['id']);
  $idlesson = json_decode($_POST['id_lezione']);
  llms_mark_complete( $user_id, $idlesson, 'lesson');
  return $user_id;
}