Upload a hashed customer list to Meta as a Custom Audience for ad targeting

Steps

1. Create a Custom Audience by POSTing to /act_{ad_account_id}/customaudiences via Graph API v22.0+, setting subtype to CUSTOM and customer_file_source to USER_PROVIDED_ONLY
2. Retrieve the audience ID from the response, then prepare your customer data by normalizing and SHA-256-hashing each PII field (email, phone, first name, last name) according to Meta's hashing specification
3. Structure the payload as an array of schema keys (e.g. EMAIL, PHONE) and a corresponding data array, encoding hashed values as hex strings
4. POST the hashed data to /{audience_id}/users with the payload, respecting the 10,000-row batch limit per request
5. Paginate additional batches via subsequent POST requests until all records are uploaded; each batch appends to the audience
6. Monitor audience delivery_status and approximate_count via a GET on the audience ID to confirm population before targeting