Hidden Fields Not Writing To Airtable

I have a system where users may create a project container, as an airtable record - and then append individual records to this container.

I have a details page configured for the top level container in which users can enter, and then add records to this project.

I am using hidden fields to assign the new records directly to the top-level container based on the ‘detail page record > field’ function. This works great when it is a customised form - but if I try and use this on the ‘add new record’ action button, it is not scraping the data to input it. I’ve tried directing it to just a simple text / long text field in airtable and get the same result. It will still scrape data from the logged in user though, just not from the details page.