This error is the gatekeeper of the downgrade world. It is a frustrating barrier that usually stems from poor error handling in the saving tools. While it serves as a necessary warning that something is wrong (either your network or the signing window), the message itself is unhelpful. My advice to anyone seeing this: Ignore the error text. Check your network, verify the signing status online, and run the tool as Administrator. Don't trust the error message to tell you what is actually wrong.
The "Error: Unable to Request SHSH" is a relic of a bygone era of iOS modding tools. While the task—requesting a signature from Apple—is complex, the error reporting is archaic. error unable to request shsh