laravel-cashier-mollie: Some Payment Methods don't work with LIVE API key, but do with TEST API key

While implementing a Donation page for our client, we ran into an issue.

While using the test-api-key, we were able to create a payment checkout process that brought us to a Mollie page where we could choose on of the two configured payment methods (configured in Mollie dashboard, “Bancontact” and “Visa”). But when using the live-api-key, the mollie checkout url skips the payment selection, and directly goes to the payment form for “Visa”.

This happens for the one-time payments, as well as for the subscriptions:

    private function handleSubscription(Donation $donation)
    {
        $plan = Plan::firstOrCreate(
            ['amount' => $this->amount],
            [
                'working_title' => $this->amount,
                'description' => "ITG Donation {$this->amount}",
                'interval' => 1,
                'period' => 'month',
                'active' => false,
            ]
        );

        $result = $donation->newSubscriptionViaMollieCheckout("subscription {$this->amount}", $plan->working_title)->create();

        return redirect($result->getTargetUrl()); // Redirect to Mollie checkout
    }

    private function handleOneTimePayment(Donation $donation)
    {
        $tax = $this->vat_number ? 0 : 21;

        $item = new \Laravel\Cashier\Charge\ChargeItemBuilder($donation);
        $item->unitPrice(money($this->amount * 100, 'EUR'));
        $item->taxPercentage($tax);
        $item->description('One Time Donation');
        $chargeItem = $item->make();

        $result = $donation->newCharge()
            ->addItem($chargeItem)
            ->create();

        return redirect($result->getTargetUrl()); // Redirect to Mollie checkout
    }

Is there a problem with our code, with the package? We are clueless as Mollie support assures us that the Web Profile and Payments configuration is set up correctly.

Thanks in advance.