If this succeeds but 3uTools fails, the issue is 3uTools-specific.
The developers release patches specifically for SHSH request errors. Go to Settings → Check for updates weekly. 3utools Error Unable To Request Shsh
: Verify if the iOS version you are trying to flash is still "signed" by Apple. If it is "Unsigned," you cannot install it unless you have previously saved SHSH blobs for that specific device. If this succeeds but 3uTools fails, the issue