Sorry David, “should” was maybe the wrong word. Apologies for that.
Breww doesn’t currently permit this, I don’t think. i.e. if we have a multipack product made up of 6 of the base product, we can’t use Breww’s “return” mechanism to bring back some (less than 6, here) of the base product. We can only return the (sold) multipack product?
Although this is something that has been asked for (FR linked above). There’s also this FR
I guess that if you’re managing to return a part of this case product, you either don’t have it set as a multiple of the base product, or you’re adjusting stock in some other way?
But currently, the price in your pricebook for a product (even if this is zero) is what Breww will use for a credit note. I think. If you want it to come up as something other than zero I guess you’ll have to put it in.