devtrackers.gg
Unfortunately, Dante Unbound for iOS is temporarily on hold due to Cert submission issues. Logging into iOS if you've linked your iOS account to another platform is disabled until iOS can receive the update.
For a more extensive write-up, you can check this PSA here:
https://www.reddit.com/r/Warframe/comments/1bp3c3l/dante_unbound_for_ios_on_hold/