is there any tutorial, documentation or hints how to add a custom form to the Payment&Review step for my custom offline payment module in Magento2 checkout process and how to connect it to the database? I have seen some tutorials that describe how to add fields to the shipping address (e.g. https://sohelrana09.wordpress.com/2015/11/28/how-to-add-custom-field-to-shipping-address-form-in-magento-2-onepage-checkout/) but that is no option for me because the solution should work even for products without shipping. Any ideas?
Thanks a lot