Facebook targets its users using their email addresses via an external data source.
That's why you must pass your users' email addresses and GDPR Opt-in to Insider before using Facebook Custom Audiences in your Architect journeys.
If your company obtains your users' consent in compliance with the local regulations, make sure to pass the GDPR opt-in field to Insider. If you want to stop collecting and processing the data of an identified user, GDPR opt-in field should have the false value. Insider cannot be held liable if these obligations are not fulfilled and reserves the right to seek compensation from your company.
To get started, read more about how to integrate Facebook.