Reinstall MacOS High Sierra after Erase

It seems the internal drive is already blank so you are free to mess with it, right?

So just try again and follow the link's instructions to the letter. You might want to start from the very scratch by resetting PRAM so the previous attempt to modify it is nuked.

To Reset PRAM: shutdown, power ON, and when you hear the status chime start pressing Option-Command-P-R keys (be prepared to do so in advance...), and keep them down until the Mac chimes a 2nd time, then let go.

Then boot to Internet Recovery by holding down Option-Command-R keys the same way and follow those instructions to bypass that flaw Apple should have fixed long time ago.

I'd use the Disk Utility to erase the internal device, not volumes under it (select View > Show All Devices) as APFS (SSD) or MacOS Extended, GUID (HDD) while in Recovery.

https://mrmacintosh.com/how-to-fix-the-recovery-server-could-not-be-contacted-error-high-sierra-recovery-is-still-online-but-broken/

You can only install HIgh Sierra on an existing High Sierra installation or older such as Sierra or older.

Macs older than High Sierra's release date will have internet recovery load Sierra, and may not see the content of the hard drive to install to except in using command-option-shift-R boot. If you have a bootable copy of HIgh Sierra on an external hard drive with nothing else on it, you can clone that.

Some people have difficulty because the time and the certificates don't match. Make sure the computer's date is set for later than High Sierra's release, but within the same year after the release of 10.13.6.

certificates may make release unavailable thread may help.