The first and foremost things to do when following an online guide are:
- See how old that guide is
- See if there are follow-up questions at the end by readers and see if the OP had followed-up, as well as how recently any of this had occurred
- Anything older than a few years as well as no activity for that time, is something you likely may not receive any feedback from
You can add comments to that web page where you are following the instructions and ask the author of this process more directly.
I see as recently as August 10, 2018 they posted a reply to someone's question which was on August 9, 2018.
In my opinion, that's the best way to get the best assistance with this installation, from the person who has posted the process.
Note that in their guide they say you will first see
exactly the error you posted, if I'm not mistaken about the problem you're seeing. And then there are additional steps to follow once you encounter that error.