blobs are a mechanism used by Apple to control the iOS versions users can install on their devices. When you click "Flash" or "Downgrade," 3uTools acts as a middleman. It sends a request to Apple's TSS (Ticket Signing Server), asking for a digital signature for a specific firmware file (IPSW) for your specific device (ECID).
If you need further help, post your exact 3uTools log (especially the HTTP status code like 404 or timeout) on forums like r/LegacyJailbreak or the 3uTools official support center. Error Unable To Request Shsh 3utools 9
Corrupt drivers can mimic SHSH errors.
For 99% of users, switching to the latest signed iOS version or disabling firewall/antivirus solves the issue immediately. blobs are a mechanism used by Apple to