Not to say it's impossible, but let's unpack this:
You want people who are scrolling on Facebook in the middle of a huge dopamine orgy to stop what they are doing and go over to your website and impulse-purchase something for $20 that they have to READ to get benefit from, from a guy they didn't even know existed 15 seconds ago?
If you think about the triggers that get people to buy, and examine popular marketing, you'll find that 99% of buyer psychology hinges on authority, social status, trust, and demonstration/proof elements. Hence "as seen on", hence tons of testimonials, hence celeb endorsements, etc etc.
You're spending a very low amount of money ($6/day). But even if you need to spend 8x6 ($48) to make one $20 sale, that could still be profitable if you have a backend / upsells. That assumes your ebook is good and people will read and implement it, and now they like you and you can sell them something else.
But no one knows if X impressions or Y clicks is "good" on Facebook, because everyone's audience and offer is different. Serious FB advertisers spend 3,4,5 figs a day.
Anyway, maybe you are going for the sale too quickly is all I was saying. You are getting 100 people per day to look at your landing page. If you gave away some bribe to get them to join an email list, maybe you could convert 8 to 20 people per day. Then you email them a few times a week with some fun stuff that ties into your ebook, with a link at the end of the email to buy the book. Maybe they need 3, 10, 50 emails before they buy. Do you really think online ads are as simple as "one ad, then they buy"? Everyone would be killing it, then.