Each asset must already exist in the media bank; this only links them to the product. Existing associations on
the product are preserved, and the new assets are added on top rather than replacing them; IDs already
associated are ignored. Fails if the product does not exist or if any listed asset ID is not found. To attach
exactly one asset, the single-asset variant that posts to {id}/assets/{assetId} is simpler; to replace the
product's entire asset set with a new list, use the PUT on {id}/assets instead.

For more information on assets in Bluestone PIM, refer to our help pages Assets
overview.