I want to update my iPhone from 8.4 to 9.3 for Testing Purpose. As 10.1 is now officially available, we are not able to update to 9.3 from setttings. As an alternative we have downloaded ipsw file of iOS 9.3 version and we are trying to update the OS 8.4 to 9.3 via iTunes. However in this process we are facing an issue. We are getting a message "TATSU declined to authorize this image on this device for this user"
From internet I found that:
The Tatsu Signing Server (TSS) is a service provided by Apple. Apple provides a list of available services at gs.apple.com. There is an Apple internal equivalent, known as Spidercab, running at tatsu-tss-internal.apple.com which is accessible only within Apple's VPN. Spidercab is used to sign internal/debug builds of iOS, including old versions that are no longer signed on production.
If anyone faced this problem and if there is any solution? I am still trying to sort this out. If anyone has updated iOS not to the latest version but to the intermediate update.