If the primary is down, users have reported success with https://wiikeys.web.app/ or the archived vault at http://vault.titlekeys.ovh/ .
However, there is a phrase that strikes frustration into the heart of every new user: title keys for wii u usb helper upd
Delete the cache folder inside your USB Helper directory. Then, re-inject the title keys. A corrupted cache will keep feeding the app old, invalid keys even after you update. If the primary is down, users have reported