Dropbox doesn't offer an FTP interface, but it does offer an API you can use for transferring files, among other operations.
It does offer typical upload and download functionality, but it sounds like that wouldn't be ideal for your scenario. One possible alternative, if you can get Internet-accessible links to the files you need to transfer, would be to use /2/files/save_url instead. That allows you to save files to Dropbox by supplying Dropbox URLs to those files, instead of downloading/uploading the data locally.
Those are links to the documentation for the HTTPS endpoints themselves, but we recommend using one of the official SDKs if possible. Those have corresponding native methods for the HTTPS endpoints. The API v2 Explorer may also be helpful.
