I've now read through this entire thread and haven't seen my specific problem addressed. I'm building a site on ZenCart which was previously built from scratch using FrontPage and Miva Merchant. The function I'm trying to put in, which brought me to BT, is:

We have one product on which we say, "Free with any book order." Our catalog is very small. We have 3 categories:

1 - Books (5 items)
2 - Brochures (11 items)
3 - Other (3 items)

The "Free with any book order" product is #16 in category 2. After carefully reading your doc, I concluded that the appropriate call was

add_prod_to_cat(1,16,”%”,100);

but when I loaded this to my site and test in the shopping cart, I get no discount at all. The crazy thing is, my first pass was backward - add_prod_to_cat(16,1,"%",100) - and the discount worked, but on the wrong item - it discounted the category 1 item.

The statement I think is correct doesn't discount at all. Before you ask, I've established that the value in master_categories_id is NOT zero. What should I be doing?? I want product 16 in category 2 to be free with purchase of ANY item in category 1.