ACFの画像をアイキャッチ画像として使う

function acf_set_featured_image( $value, $post_id, $field ){
  if($value != ''){
    //Add the value which is the image ID to the _thumbnail_id meta data for the current post
    add_post_meta($post_id, '_thumbnail_id', $value);
  }
  return $value;
}
  
// acf/update_value/name={$field_name} - filter for a specific field based on it's name
add_filter('acf/update_value/name=フィールド名', 'acf_set_featured_image', 10, 3);