My AI connection fails with an Authentication Error.

If the sign-in window ends on a page that reads “Authentication Error. This action could not be completed. Please close the window and try again,” the cause is almost always Advanced Data Protection on your Apple account.

Advanced Data Protection is an Apple security feature that keeps your iCloud encryption keys on your own devices only. That is good for privacy, but it also blocks the web sign-in the AI connection uses, so the connection cannot finish. This is an Apple limitation, not something Parameter can work around from its side.

To connect, turn Advanced Data Protection off. Open Settings, tap your name at the top, then iCloud, then Advanced Data Protection, and turn it off. Then try the connection again. Turning it off is a real tradeoff, since it is a security feature, so whether the AI connection is worth it is your call.

The rest of the app works normally with Advanced Data Protection left on. Building, running, and logging workouts, and syncing between your own devices, are all unaffected. Only the AI connection needs it off.