protected function buildPayload()
    {
        return array_filter([
            'billing_cycle_anchor' => $this->billingCycleAnchor,
            'coupon' => $this->coupon,
            'metadata' => $this->metadata,
            'plan' => $this->plan,
            'quantity' => $this->quantity,
            'tax_percent' => $this->getTaxPercentageForPayload(),
            'trial_end' => $this->getTrialEndForPayload(),
        ]);
    }