Selling a Next.js courses: help me figuring the marketing

Hey folks,

I am an experienced web developer and data science consultant, own a CS degree, got around 6 years of experience with Next.js (yeah, I was using it before it was cool), and laid down a theory of server-side rendering leading to significant optimizations (look for "segmented rendering").

I like sharing content, usually for free. Lately, I've also tried to produce even more valuable and detailed content, which is however only possible to achieve if I make it paid. I'd still like to be not too expensive, which means having a volume strategy where I sell many cheap courses.

But the thing is that, I am not great at marketing. I try to get better, to learn the basics of design, copywriting marketing channels. I am progressing but very slowly.

Therefore, I am calling the Indie Hacker community for help.

Here is the lading page for Next.js Patterns, a collection of paid courses around Next.js : https://nextjspatterns.com/

And here is the landing page for a specific pattern, the first in the series : https://course.nextjspatterns.com/manage-client-only-code-in-next-js-with-react-browser-components

I've cumulated a gross revenue of... 25€, in 2 sales (one early version for 5€ and a full version for 20€).

I am running Google Ads, and I've published an article linking to the site that got around 1K views : https://medium.com/@eric.burel/how-to-get-rid-of-window-is-not-defined-and-hydration-mismatch-errors-in-next-js-567cc51b4a17. I am also translating my articles from English to French in order to have a better visibility locally.

I've slightly lowered the price, to 15€, because I figured the first course I wrote, about client-only code, happens to be more an upsell product rather than a "discovery product" (I couldn't figure the translation for "produit d'appel" in English sorry), so I should have started with more common topics like security or testing. That's what I'll do for the next courses.

So, my question is: what can I improve?