I have edited the rest of my posts, all logs and configs should now be using code blocks.
I am quite sure that I have filled in my credentials appropriately, and looking at this other post Example Caddyfile for acme w INWX / dns challenge, it seems that I was not the only one encountering this kind of issue. For now I have switched to Cloudflare for DNS hosting, and the certification process worked. I will open a ticket on the module’s Github page to see what may be wrong with the initial setup.
Anyway, thanks for the help !