Disconnect your Mac from the internet. Open Terminal during installation and change the system date back to 2017 using the command date 0101010117 . "The installer payload failed signature verification"
This is another variation of the expired certificate issue. Ensure your Wi-Fi is completely turned off so the Mac doesn’t sync with modern network time, and use the Terminal date rollback command shown above. download macos sierra 1012 dmg file install
Now that your bootable media is prepared, you can proceed to install the operating system. Booting from the USB Drive Shut down the target Mac completely. Disconnect your Mac from the internet
Open the mounted disk and double-click the InstallMacOSX.pkg file. download macos sierra 1012 dmg file install