The product ID is a unique identifier that appears in your product feed and is also used in the tags. If you have two products with the same ID, only one will be imported.
It’s not an issue if you do have duplicate product IDs; the engine will still properly optimize the campaign.
However, as we will only pick one product to import, the total number imported will differ from the total number of items shown in your feed.
If one of the products is a variant (eg. different colour or size), we will import the main parent product and associate all variances to it.
If you want us to import and use two distinct products that share the same ID, you will need to assign a unique product ID for each.