Can't restore or update IPhone - TATSU declined to authorize I'm attempting to either restore or update an iPhone 5 which won't boot. It's stuck on the apple logo boot screen. Hard reset does nothing.

I have tried normal restore mode via iTunes and DFU mode. 

I'm signed into iTunes as the same apple ID as the phone.

I've authorized the mac for this apple ID in iTunes.

each time I try and either do update or restore I get the following error from iTunes:

iphone could not be restored (updated). TATSU declined to authorize this image on this device for this user.

Anything else I can try? it does not matter if I lose the data on the phone. Just needs to work again.

Also is there a way to view the boot sequence from my mac or the phone either via terminal or xcode or something so I can see where it's hanging in the boot sequence?
for anyone else who comes across this or something similar. It turned out that my hosts file had an entry to gs.apple.com which was causing apple's signing (TATSU) server request to fail with their not so helpful error message. 

So you need to check your hosts file on the computer you are running iTunes on to see if there are any entries to gs.apple.com and then either remove those lines or comment them out by placing a # at the start of the line. 

like so #gs.apple.com 74.454.656.343  easiest way is via terminal. look up how to edit host file if you don't know how. on my mac the host file was located at /etc/hosts  once in terminal: sudo nano /etc/hosts will open an editor, once changed control x will exit, type y then enter when prompted to save your changes to the hosts file. all done.