recovery server could not be contacted
I am selling my 2017 MacBook Air and have erased MackintoshHD but can't re.install - keep getting 'the recovery server could not be contacted' I've re.started in recovery mode, gone into Utilities/Terminal and added the date to be sure that wasn't the problem - but still getting the message and still can't re.install High Sierra ... help please!
MacBook Air 13″, macOS 10.14