When all else fails, use the command-line tool tsschecker (the same engine 3uTools uses internally). This tells you if the problem is 3uTools itself or Apple’s server.
Steps:
Solution: If unsigned, you cannot request SHSH via normal methods. You can only save “on-board” blobs if your device is already running that version (using a jailbreak tool like System Info or blobsaver). How To Fix Error Unable To Request Shsh On 3utools When
First, let’s decode the jargon.
When 3uTools says it is “Unable to request SHSH,” it means the software tried to ask Apple’s servers (or a local cache) for a valid signature to install a particular iOS firmware, but Apple refused or the request could not be completed. When all else fails, use the command-line tool
This most often happens when: