Dropbox limits the number of files you can permanently delete at one time. If you see an error that says "Too many files to permanently delete," you just need to permanently delete files in smaller chunks.
Permanently deleted files can never be recovered, so please be extremely careful when you use this feature.
Deleted and permanently deleted files do not count against your storage quota. Permanently deleting files after they have already been deleted will not free any more space in your Dropbox.
Deleted files are permanently deleted automatically after 30 days, unless you have our extended version history feature or a Dropbox Business account.