You can only use the gravity form add-on for Fancy Product Designer in non-WooCommerce products. You will also need the Fancy Product Designer Plus Add-on.
First you have to add an extra "Single Line Text" field to your form. This field is used to store the data for the order.
Open the field options and click on the "Appearance" tab and enter "fpd-order" in the Custom CSS class input.
Last but not least go to the Advanced tab and enable "Hidden" show this field is not showing up in the form.
Optional: Display a price (since FPD PLUS V1.2.0)
If you want to display the price of the product designer in the form, you need to add another "Single Line Text" to the form and enter fpd-price in the Custom CSS class.
Connect Fancy Product Designer with a GF form
Last but not least you have to use another shortcode to display the product designer in any post or page (no WooCommerce products) and to connect the product designer to a form.
Put this shortcode anywhere in the page. The page needs to include also the GF form that you set up for the product designer.