private function sync_plan_if_not_exist( $plan_id ) {
            $plan = self::_get_plan_by_id( $plan_id );

            if ( is_object( $plan ) ) {
                // Plan already exists.
                return $plan;
            }

            $plan = $this->fetch_plan_by_id( $plan_id );

            if ( $plan instanceof FS_Plugin_Plan ) {
                $this->_plans[] = $plan;
                $this->_store_plans();

                return $plan;
            }

            return $plan;
        }