Custom Field Updation with API v2

custom_field_updation_with_api_v2.js

<script> 
  var api_key = "API-KEY";
  
  function update_custom_field(ticket_field_id, callback){
    var payload = '{"custom_fields":{"account": "{{ticket.company.account}}"}}';
    var url = 'https://'+window.location.hostname+window.location.pathname.replace('/helpdesk','/api/v2')
      jQuery.ajax({
        type: 'PUT',
        url: url,
        data : payload,
        contentType: 'application/json',
        headers: {"Authorization": "Basic " + btoa(api_key+":"+'X')},
        success: function(data){
          callback(ticket_field_id);
        },
        error: function(jqxhr, text_status, error_thrown) {
          console.log(text_status, error_thrown);
          callback(ticket_field_id);
        }
      });
  }
  
  function update_ticket_field(ticket_field_id){
      jQuery('#'+ticket_field_id).val("{{ticket.company.account}}");
  }
  
  update_custom_field('CUSTOM-FIELD-ID', update_ticket_field);
    
</script>