functions.php

<?php

/**
 * Override ap_user_can_ask function.
 *
 * @param string|boolean $ret Return empty string to continue operation.
 * @param integer $user_id
 * @return string|false
 */
function my_filter_ap_user_can_ask( $ret, $user_id ) {
  $allow = true;

  $private_categories = array( 'literasi-perbendaharaan' ); // categories subscribers cannot see
  
  if ( is_single() ) {
    $cats = wp_get_object_terms( get_queried_object()->ID, ‘question_category’, array( 'fields' => 'slugs' ) ); // get the categories associated to the required post
    if ( array_intersect( $private_categories, $cats ) ) {    
      // post has a reserved category, let’s check user
      $allow = check_user();
    }
  } elseif ( is_tax( 'question_category', $private_categories ) ) {
    // the archive for one of private categories is required, let’s check user
    $allow = check_user();
  }

  // Return empty string to allow normal operation.
  return $allow ? '' : false;
}
add_filter( 'ap_user_can_ask', 'my_filter_ap_user_can_ask' );