This may not be the most sophisticated idea, but if you are in a hurry, you can opt to download the html and do a little web scraping.
Steps
1. Go to your product portal and select create a product:
2. There you will find a "Folder" selection box, and click inspect the page from your browser:
3. In the html of the page you will find the name of the Folder and its respective ID.
4. Finally by downloading/copying the html of the page and doing a little web scraping you will be able to get all folder IDs with their respective names.
When I make this API call, the hs_folder_id returns as null. Any suggestions? I was hopeful and thought I had a solution that I've been spending weeks trying to find, but ran into this blocker. Any insight would be greatly appreciated!!!