public function cancel(string $id, bool $atPeriodEnd)
    {
        // Log Debug
        $this->flow->getLogger()->debug("Cancelling Subscription $id" . ($atPeriodEnd ? ' at period end.' : '.'));

        return $this->make(
            $this->flow->send(
                'post',
                $this->endpoint . '/cancel',
                [
                    'subscriptionId' => $id,
                    'at_period_end' => (int) $atPeriodEnd,
                ]
            )
        );
    }