$this->set( 'order_key', $this->generate_order_key() );
	}

	/**
	 * Calculate the next payment due date
	 *
	 * @since 3.10.0
	 * @since 3.12.0 Unknown.
	 * @since 3.37.6 Now uses the last successful transaction time to calculate from when the previously
	 *               stored next payment date is in the future.
	 * @since 4.9.0 Fix comparison for PHP8 compat.
	 * @since 5.3.0 Determine if a limited order has ended based on number of remaining payments in favor of current date/time.
	 *
	 * @param string $format PHP date format used to format the returned date string.
	 * @return string The formatted next payment due date or an empty string when there is no next payment.
	 */
	private function calculate_next_payment_date( $format = 'Y-m-d H:i:s' ) {

		// If the limited plan has already ended return early.
		$remaining = $this->get_remaining_payments();
		if ( 0 === $remaining ) {
			// This filter is documented below.
			return apply_filters( 'llms_order_calculate_next_payment_date', '', $format, $this );
		}