* @return int|WP_Error Timestamp of the scheduled event or an error object.
	 */
	protected function schedule_single_processor( $processor, $id ) {

		$hook = 'llms_dispatch_notification_processor_async';
		$args = array( $id );

		// Save items in the queue.
		$processor->save();

		// Check if there's already a scheduled event.
		$timestamp = as_next_scheduled_action( $hook, $args );

		// If there's no event scheduled already, schedule one.
		if ( ! $timestamp ) {

			$timestamp = llms_current_time( 'timestamp', 1 );

			// Error encountered scheduling the event.
			if ( ! as_schedule_single_action( $timestamp, $hook, $args ) ) {
				$timestamp = new WP_Error(
					'schedule-error',
					// Translators: %s = Processor ID.
					sprintf( __( 'There was an error dispatching the "%s" processor.', 'lifterlms' ), $id )
				);
			}
		}

		return $timestamp;