This attribute contains the number of identical products in a multipack.
If it is possible to submit multipacks the 'multipack' attribute is required for all countries except Austria, Denmark, Belgium, Canada, Norway, Sweden, India, Mexico, Poland, Russia and Turkey.
If your feed contains multipacks you have to notice the following informations. First of all check if your price attribute contains the total price of all items of your multipack. Additionally, the main image of your multipack must show only the base item of your multipack (e.g. one glass of wine, not six of them). The 'multipack' attribute contains the number of manufacturer-defined multipacks that are bundled if the base item of your multipack is a manufacturer-defined multipack. Furthermore you should provide the unique product identifiers for your manufacturer-defined multipack.
The 'multipack' attribute does NOT contain the number of items in a manufacturer-defined multipack, but rather the number of items in merchant-defined multipack, i.e. items you packed together.
Multipacks are multiple items of the same kind packed together, whereas bundles are several different items, that belong together.