Sometimes, reverting to Apple's official tool can resolve issues caused by third-party software. Ensure you have a backup, then attempt to restore your device to the latest signed iOS version using iTunes. This will most likely resolve any software corruption, but it will also update your device to the newest iOS version.
If you're still encountering the error, try using a different computer or device to see if the issue is specific to your current setup. How To Fix Error Unable To Request Shsh On 3utools When
If you are attempting to downgrade and have previously saved SHSH blobs: Sometimes, reverting to Apple's official tool can resolve