In signup form the association between the coupon and selected product is not checked. As usual we expect if a user using an unrelated coupon for a product in signup form, he / she should receive an error like this "This coupon belongs to another product" but can successfully signup the code with any product. Is it a bug or unimplemented feature? Any idea? Have anybody checked it yet? Thanks
I tested this. When you use a coupon that does not apply to the product the sale is completed but no discount is applied. I do think your idea is good. If an invalid coupon code is used an error message should alert the user. I will add this to the aMember BugTracker and reference this post.