public function get_revenue( $period ) {

		$query     = $this->orders_query( -1 );
		$order_ids = wp_list_pluck( $query->posts, 'ID' );

		$revenue = 0;

		if ( $order_ids ) {

			$order_ids = implode( ',', $order_ids );

			global $wpdb;
			// phpcs:disable WordPress.DB.PreparedSQL.InterpolatedNotPrepared
			$revenue = $wpdb->get_var(
				$wpdb->prepare(
					"SELECT SUM( m2.meta_value )
				 FROM $wpdb->posts AS p
				 LEFT JOIN $wpdb->postmeta AS m1 ON m1.post_id = p.ID AND m1.meta_key = '_llms_order_id' -- join for the ID
				 LEFT JOIN $wpdb->postmeta AS m2 ON m2.post_id = p.ID AND m2.meta_key = '_llms_amount'-- get the actual amounts
				 WHERE p.post_type = 'llms_transaction'
				   AND p.post_status = 'llms-txn-succeeded'
				   AND m1.meta_value IN ({$order_ids})
				   AND p.post_modified BETWEEN %s AND %s
				;",
					$this->get_date( $period, 'start' ),
					$this->get_date( $period, 'end' )
				)
			);// db call ok; no-cache ok.
			// phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared

			if ( is_null( $revenue ) ) {
				$revenue = 0;
			}
		}

		return apply_filters( 'llms_course_data_get_revenue', $revenue, $period, $this );

	}