If you want, tell me: the exact error log text from 3uTools (or a screenshot) and your Windows version + device model and iOS version; I’ll give targeted next steps.
If you are trying to save SHSH2 blobs for , the process has changed. Apple introduced a "Rootless" file system. Standard SHSH requests via 3uTools often fail on these newer firmware versions if the device is not properly prepared.
The most common reason is attempting to install an iOS version that Apple is no longer signing. Once signing is closed, a standard restore to that version is impossible without previously saved SHSH blobs. Outdated Software: