Woocommerce custom fields on checkout page (checkbox)

Hi there,

I would like to customize my checkout page built with Woocommerce.

Since it’s a music shop, I would like to insert some checkout boxes to precise for what the product will be used (related to music licenses).

I found these serial of tutorial : https://uploadwp.com/customizing-the-woocommerce-checkout-page/

I read the topic called “Adding Custom Fields to the WooCommerce Checkout Page” on this page.

My problem is that I want to add multiple checkboxes with at least one choice done. If not, then there is an error message.

How to transform this code to fit with my requirement ? Or is there any other tutorial for that ?

Thanks for your help ??

P.S. : I’m not interested by any plugin, I want to understand how to make that by myself.