I was on High Sierra beta and decided to sell my 2015 MacBook Pro since I upgraded to the 2017 touchbar one. I created a bootable Installer of Sierra on my flash drive and tried to install Sierra on the 2015 Pro to sell and I got the error while preparing installation in the final three seconds of the installation. I read online sometimes it’s an issue with the computers time so I changed it to my time in the terminal. Second time around same error. Now my MacBook is bricked. Can’t sell it now or use it. What do I do?