php - Receiving empty data on ajax request in spite of available data -

i trying sub-category list of category ajax request through admin-ajax.php. categories under custom post type. each category has sub categories. ajax request returns no data in console.

jquery.ajax({     type: 'post',     url: classipress_params.ajax_url + "?action=dropdown-child-categories",     datatype: "json",     data: {         cat_id : category_id     },     //show loading when dropdown changed     beforesend: function() {         ...     },     //stop showing loading when process complete     complete: function() {         .....     },     error: function(xmlhttprequest, textstatus, errorthrown){         ....     },     // if data retrieved, store in html     success: function( data ) {         // child categories found build , display them         if ( data.success === true ) {             console.log(data);              ....         }     } }); 

am doing wrong? category_id okay, tested that. result in console:

{     success: true,      html: "" } 

try changing action hook name :

add_action( 'wp_ajax_nopriv_cp_addnew_dropdown_child_categories', 'cp_addnew_dropdown_child_categories' ); add_action( 'wp_ajax_cp_addnew_dropdown_child_categories', 'cp_addnew_dropdown_child_categories' );