Free Product With Specific Purchase

I would like to offer a free photo cushion with the purchase of a photo blanket (I already offer the products individually) and I would like them to use a code to do so. Can you advise the best way of doing this? I looked at special coupons but I can't work out how to charge the normal price for the blanket with the various options available (size and extra photos on it) which is already created as a collection, and add the cushion for free?

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There is no way of doing that with a coupon code. I can not think of a workaround unless you just include it with the product.

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