@crispypop If I'm following correctly, it looks like you need to forward event records that include other attributes like hashed email, phone, etc. to the Meta Conversions API. If you're using Advanced Matching, or if you set the client-side Meta Pixel to auto-send form data, you may already be sending some of that data via the pixel.
Option 1: for authenticated visitors, read the source data (email, etc), send it in a sendEvent call from Web SDK, then send to Meta in Event Forwarding with the cAPI extension.
Option 2: collect event IDs and all required event attributes as they occur client-side (using your systems to collect & store), combine them with the other data you have & want to send to Meta, then use the Edge Network Server API to stream or batch send those event records (with all needed data) to Adobe, then use EF + Meta cAPI extension to stream them to the API.
Option 3: if you know you have the attributes you need stored in a Platform dataset, and you have a unique identifier you can use as the key to query for those attributes, you might be able to query a Platform API to retrieve those attributes, then combine them with your event record data, and send to Edge Network Server API as above. Querying Platform APIs from Event Forwarding for this use case is not currently available or supported, so in concept that would be done from your systems, then send to Edge API, etc.
Many customers simply work with their front end team(s) to make the additional attributes available in the browser and the events, and go from there.