An outdated 3uTools client may have broken API endpoints. Uninstall, then download the latest version from the official site. Older builds often fail to request blobs for new iOS versions because Apple changes its TSS protocol. A fresh install resets corrupted configuration files.

SHSH blobs are tiny files that are unique to your device and serve as Apple's official "stamp of approval" for a specific iOS version. They ensure only authorized software runs on your iPhone or iPad. While it's beneficial that 3uTools tries to get the latest signature from Apple every time, this is where the problem starts.