Hello,
Our plugin uses the default WooCommerce add-to-cart product validation, and this appears to be causing the issue you’re experiencing.
Given that your product’s price is set to zero or is empty, the WooCommerce method “is_purchasable” returns ‘false’. Consequently, you wouldn’t be able to add these products to the cart directly from your shop’s product listing or product page. We’ve verified this on your shop.
To resolve this, you may want to consider using the “woocommerce_is_purchasable” hook. This could provide a workaround for your situation by altering the conditions under which a product is deemed purchasable. Bear in mind, though, that you may need some custom coding to adjust this setting according to your needs.
We hope this information helps as the issue lies outside the scope of our plugin.