Create one or many CatalogItem. If a CatalogItem with the same identifier (SKU, product ID, or both, depending on your catalog's item key setting) already exists, it is updated instead of rejected, and its existing ID is returned. Fields you provide replace the stored values, except dutyTaxFeeConfiguration and productComposition, which are only set when the item is first created. Fields you leave out keep their stored values. Because of this, repeating the same call (for example, after a timeout) is safe.