Inpsyde\MultilingualPress\API\SiteRelations::insert_relations PHP Method

    public function insert_relations($base_site_id, array $site_ids);

 /**
  * Updating Site Relations for new sites.
  *
  * @param  int $blog_id
  * @return int Number of affected rows.
  */
 private function update_relation($blog_id)
 {
     if (empty($_POST['related_blogs'])) {
         return 0;
     }
     $new_related = (array) $_POST['related_blogs'];
     $related = array_map('intval', $new_related);
     return $this->site_relation->insert_relations($blog_id, $related);
 }