I need to show specific users with specific ads on facebook which are specifically created for them in such a way that two users cannot share same ad. I found extern_id parameter that can be added while adding custom audience, which will be used as a matching parameter while showing ads to user. There are two things that I have doubt with:
What would be the value of extern_id, my assumption is - it is the id of product in product feed, so that while matching audience user with product feed it specifically picks the product with id as extern_id. Is this assumption correct?
While uploading custom audience data using Business manager, I tried adding extern_id as one of the columns, but was not able to upload the file, as it is not taking extern_id as a field available to be uploaded with audience data. But in documentation for adding custom audience: https://developers.facebook.com/docs/marketing-api/audiences-api, extern_id can be added with other params.
There is no way to create ads that target one single user. There are limits on the minimum audience size to prevent this, and you should check that the ads you are trying to create are in line with FB's ad policy.