i have the code that can add a post in a custom post type but adding the category is not working.

$args = array(
    'post_title' => $title ,
    'post_status'   => 'publish',
    'post_type' => 'mypost' 
);

$post_id = wp_insert_post($args);

$category_ids = array(38,39);
wp_set_post_categories( $post_id, $category_ids, 'category');