iPhone 15 unable to update to iOS 26.6.1

Can't update iPhone 15 to iOS 26.6.1

Dear All,

We have two iPhone 15 at the moment, and both don't upgrade to iOS 26.6.1. One of them is currently on 26.4.2, the other one on is on 26.6

It always says "Unable to Verify Update. iOS 26.6.1 is temporarily unavailable. Try again later." This is going on for days now.

I have tried on our house WLAN, used my Google Pixel 10 pro as Hotspot and downloaded via that.

I have tried to connect one of the iPhone to our Macbook and do the update via Finder. It does download it, but then says "The iPhone "<iphone name>" could not be updated. Declined to authorize this image on this device for this user."

I have used different iCloud accounts. In the whole process, I have done factory resets numerous times, downloaded the updates numerous times, deleted the downloaded files after it failed and re-downloaded, factory reset again,...

What's also "funny": The size of the update seems to vary all the time and I had everything between ~400 MB and 11.6 GB (in the storage and update sections of the settings on the iPhone).

Why do we need the update so urgently? My daughter wants to upgrade from her iPhone 13, but I haven't managed yet to transfer the data from the old phone, because any transfer attempt wants to have the update first (when phones are next to each other, and also when local backup via Macbook), but the current update doesn't run on the new phone.

Does anyone have any idea?

Best wishes,

Andre