Are you trying to or just restore to the current version?
This is the most common cause. You cannot flash a firmware version that is not signed unless you have previously saved your SHSH blobs. Open 3uTools and go to the section. Look at the list of available firmwares for your device. i unable to request shsh 3utools fix install
3uTools must connect to Apple’s TSS servers to request the SHSH blobs. If your connection is blocked, the request will time out. Are you trying to or just restore to the current version
Proxies and VPNs often interfere with the handshake between 3uTools and Apple. i unable to request shsh 3utools fix install
Check the column. If it says "No Signing," you cannot request SHSH for that version.
Put your device into (Device Firmware Update) manually.