D&D Beyond is a fantastic service which allows you to purchase official 5e content, and access it anywhere. It takes the collective rule books and paper of in-person tabletop gaming, and helps you to move as much of it online as you want- similar to a real VTT!
D&D Beyond does not allow use of their API without authorization, per their Terms of Service. Fortunately, The Forge VTT has received permission to use their API, for the purposes of D&D Beyond integration.
To be clear, The Forge VTT does not store 5e data within its integration. Rather, it allows users to access the content they own, and import it personally into The Forge. This helpfully ensures that no matter what, the user owns the content being imported- even when issues occur with the importer. Without ownership of this content, the user will have nothing to import.
Unfortunately, this does mean that content imported via D&D Beyond must be stored within the user’s game and asset storage. We advise having plenty of spare data available in both, before importing- and do not recommend importing everything from D&D Beyond at once.