just pay shipping

Hi,

You could create a 100% coupon. You could activate its auto load setting if you want it to apply automatically to the users carts.

Hi,

So let's recap first. You want the amount of the products to be paid upon delivery only when a specific shipping method is selected. And in that case, only the shipping method cost should be paid on the website. Is that correct ?

I don't see a way to do that. It would require the development of a custom plugin to add one or two extra rows between the sub total and the total to remove the sub total, and this only when a specific shipping method is selected.
A developer could base himself on the global cart fee plugin for that specific development:
www.hikashop.com/marketplace/product/224-global-cart-fee.html
A normal PHP developer should be able to do that for you. We could also work on this for you if you want. If you're interested, please go through our contact form to request a quote: www.hikashop.com/support/contact-us.html