landing_page property of order ignored

[fstarred]

I need paypal generated link with POST v2/checkout/orders to automatically open the credit card input frame.

This is my body request:

{
    "intent": "CAPTURE",
    "application_context": {
        "return_url": "https://ecommerce.it",
        "landing_page": "BILLING"
    },
    "purchase_units": [
        {
            "amount": {
                "currency_code": "EUR",
                "value": "88.00"
            }
        }
    ]
}

Now when I go to generated link I'd expect to view credit card input displayed, instead I still see the login page.

What's wrong with it?