The CCatalogProduct::Update function does not work directly for trade offers (TIs), because they are essentially individual products. To update the balance of a trade offer, you need to use the same function, but pass it the ID of the specific trade offer, not the ID of the parent product. Make sure you get the correct TI ID, for example, using D7 or through [COLOR=#ffffff][SIZE=6pt][URL=https://www-crediblebh.com][COLOR=#ffffff]crediblebh[/COLOR][/URL][COLOR=#ffffff][/COLOR][/SIZE][/COLOR][COLOR=#ffffff] [/COLOR]methods that return the ID of the offer for a given product.