The most common identifiers that channels require are: the Brand, The manufacturer Part Number (MPN) and the Global Trade Identification Number (GTIN). The identifiers required on each channel vary, some might ask for one of the three while other could ask for all three.
1. Brand - The brand name of each product.
Google, for example, requires you to add this field to your feed in all cases. The only exception is for custom-made items where you have set the ‘identifier exist’ field to ‘false’. But you might as well add your own brand if you offer custom made products.
2. MPN - A unique identifier issued by the manufacturer.
If you have the GTIN in your feed, the MPN is not mandatory. Without GTIN, Google does require you to add MPN & Brand. The exception for custom goods applies here as well.
3. GTIN - This is the numerical version of the bar code.
It is called UPC in the US and EAN in Europe. A unique ID according to international standards. GTIN is an identifier that is created by GS1, an international non-profit organization.
Google has a database with most of the world’s GTINs. If you include the GTIN for each product in your feed, Google can identify each product and knows all product specs exactly. Also: if you provide the wrong GTIN, Google will know instantly and they will disapprove that product.