Now that we've identified the possible causes, let's move on to the troubleshooting steps to fix the error:
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. How To Fix Error Unable To Request Shsh On 3utools When
If the version and you’ve tried all steps above, reinstall 3uTools completely and try on a different PC or Mac (using a different network). Now that we've identified the possible causes, let's
If the iOS version you are selecting is no longer being signed by Apple, 3uTools cannot request an SHSH blob for it. Apple stops signing older iOS versions shortly after a new version is released. How To Fix Error Unable To Request Shsh On 3utools When
Apple only allows SHSH requests for the latest iOS version (usually).