I think I got that sorted. The post should be published for this to work as I understand from my tests. So I created a test post, published it and the shortcode worked. But here is a question; suppose I want to show more than one product. Would the shortcode separator be a comma or a +, [DFR: product?p=xxx,yyy,zzz] or [DFR: product?p=xxx+yyy+zzz]?