Webflow direct Checkout not working

Hi,

I used a Code Snippet from Shopify dynamic Button for the direct Checkout. I know it´s not liquify direct, but maybe somebody knows what to do.

The direct checkout (f.e. works when I have something in the Cart, but doesn´t work when there isn´t something in the cart. So I think there is a problem with ids etc...

Here the code I used:
{% if product.available %}
<!-- Produktformular beginnt -->
{% form 'product', product, class: 'product-form' %}
<input type="hidden" name="id" value="{{ product.variants.first.id }}" />
{{ form | payment_button }}
{% endform %}
{% endif %}