Get child of parent categories in wordpress rest api and json method:
Paste below code in functions.php
/* get sub categories */
add_action( 'rest_api_init', function () {
register_rest_route( 'yourgoodname', '/subcategories/(?P<id>\d+)', array(
'methods' => 'GET',
'callback' => 'my_sub_category_func',
) );
} );
function my_sub_category_func( $data ) {
$useableid = $data['id'];
$parent = $data->get_param( 'parent' );
sub_category_menu($parent);
}
function sub_category_menu($parentcatslug){
$category = get_category_by_slug( $parentcatslug );
$args = array(
'type' => 'store',
'child_of' => $category->term_id,
'orderby' => 'ID',
'order' => 'ASC',
'hide_empty' => FALSE,
'hierarchical' => 1,
'taxonomy' => 'category',
);
$child_categories = get_categories($args );
$category_list = array();
if ( !empty ( $child_categories ) ){
foreach ( $child_categories as $child_category ){
$category_list[] = array('slug' => $child_category->slug, 'name' => $child_category->name, 'id' => $child_category->term_id);
}
}
echo json_encode($category_list);
}
Fetch using this url below (don’t forget to change domain name to your site name)
https://domain.com/wp-json/yourgoodname/subcategories/1?parent=parent_category_slug 