Hi @wax
I believe the article you gave me is used on the my-account page, not the checkout page. If you want to add it on the checkout page, I believe the link I gave you is the proper one. In the order process, you can update the field by using the update_field()
function. Unfortunately, I’m not sure which hook you need to use. In this case, could you please ask the WooCommerce support instead?
Thanks 🙂