AJAX retorna json mas não exibe

Boa noite. Estou com problemas pra identificar o porque do código abaixo retornar a mensagem corretamente e não entrar no método success: function(){}

/** Dinamic selects */

 $('.call_ajax_on_change').on('change', function(){
 /** Define action */
 if ($(this).attr('id')==='id_categoria') {
 var action = 'action=search_for_sub1&id_categoria=' + $(this).val();
 } else if($(this).attr('id')==='id_sub1') {
 var action = 'action=search_for_sub2&id_sub1=' + $(this).val();
 } else {
 var action = 'action=search_for_sub3&id_sub2=' + $(this).val();
 }

 /** Ajax */
 $.ajax({
 url: './ajax/dinamic_select.php',
 type: 'post',
 data: action,
 dataType: 'josn',
 success: function(callback){
 //alert(callback.success);
 $.each(callback.success,function(){
 /** Interaction and generate values for selects */
 /** Read in a select with id id_sub1 */
 //if ($(this).attr('id')==='id_categoria') {
 alert(callback.success);
 $('#id_sub1').prop('disabled', false).html(ret.success);
 $('#id_sub2').empty().attr('disabled', true);
 $('#id_sub3').empty().attr('disabled', true);
 /*}else {

 }*/
 });
 }
 });
 });

PHP

<?php
/** @package Config.inc.php */

require_once '../_app/Config.inc.php';

/** @var array All data coming from $_POST form */
$post_data = filter_input_array(INPUT_POST, FILTER_DEFAULT);

if($post_data['action']=='search_for_sub1'):

 $composer_select_dinamical = new ContentDinamicForSelects();
 if($composer_select_dinamical->readSub1($post_data['id_categoria']) != ''):
 $array_data = "<option value=\"0\">Selecione</option>";
 foreach($composer_select_dinamical->readSub1($post_data['id_categoria']) as $Sub1):
 $array_data .= "<option value=\"{$Sub1->id}\">{$Sub1->nome}</option>";
 endforeach;

 $success = ['success' => $array_data];
 echo json_encode($success);
 else:
 $success = ['success' => '<option value="0">Nenhuma sub de nível 1 encontrada</option>'];
 echo json_encode($success);
 endif;
endif;