In WP Admin -> WPLMS -> Misc. -> Direct checkout I have "skip product page" ENABLED but "take this course" button redirect to product page nevertheless.
Mmmm, I think I have found where was my error.
I linked the course to the product in the course edit page, but I had not linked the product to the course in the product edit page.
Question: have I to always link course to project and viceversa, right?