I’m trying to create a Stripe Checkout Session for subscriptions, but I’m encountering an error stating “Received unknown parameter: subscription_data[backdate_start_date]”. Here is the relevant part of my code:

public function createCheckoutSession($customerId, $priceId, $isSubscription = false)
    {
        $now = Carbon::parse('2024-03-01');
        $financialYearStart = Carbon::createFromDate($now->year, 7, 1);
        $financialYearEnd = Carbon::createFromDate($now->year + 1, 6, 30);

        $sessionParams = [
            'payment_method_types' => ['card'],
            'customer' => $customerId,
            'line_items' => [[
                'price' => $priceId,
                'quantity' => 1,
            ]],
            'success_url' => url('https://test/payment/success?session_id={CHECKOUT_SESSION_ID}'),
            'cancel_url' => url('https://test/payment/cancel'),
            'mode' => $isSubscription ? 'subscription' : 'payment',
            'subscription_data' => [],
        ];

        if ($isSubscription) {
            if ($now->month == 6) {
                // User starts in June, calculate remaining days in June for trial period
                $trialEndDate = Carbon::createFromDate($now->year, 6, 30)->endOfDay();
                $sessionParams['subscription_data']['trial_end'] = $trialEndDate->timestamp;
            } else {
                // User starts before June, set the backdate start date
                $backdateStartDate = $financialYearStart->subYear()->timestamp;
                $billingCycleAnchor = $financialYearStart->timestamp;
                $sessionParams['subscription_data']['backdate_start_date'] = $backdateStartDate;
                $sessionParams['subscription_data']['billing_cycle_anchor'] = $billingCycleAnchor;
                Log::info('Setting backdate_start_date and billing_cycle_anchor for before June:', [
                    'backdate_start_date' => $sessionParams['subscription_data']['backdate_start_date'],
                    'billing_cycle_anchor' => $sessionParams['subscription_data']['billing_cycle_anchor']
                ]);
            }
        }
        Log::info('Stripe session params:', ['sessionParams' => $sessionParams]);
        return $this->stripe->checkout->sessions->create($sessionParams);
    }

Error Log:
Error processing payment: Received unknown parameter: subscription_data[backdate_start_date]

According to the Stripe documentation, backdate_start_date is a valid parameter when creating a subscription. Why am I receiving this error, and how can I correctly set a past start date for a subscription using Stripe’s Checkout Session?