reinstalling macOS

I have a 2017 MacBook Pro 15" that I wish to trade in. I have erased the hard drive using Disk Utilities and I am now trying to restore the macOS. I have followed instructions as per the Apple Support website and all seems to go smoothly. I get to the point where the computer indicated that Sierra will be installed and I click continue. The process runs smoothly for about 6 minutes but with seconds to go there is an error message 'An error occurred while preparing the installation. Try running this application again.' But this is unsuccessful. Any thoughts about what to do next, other than go to a commercial Apple repair shop? Thanks Rick