Hi Herman,
I also wanted to show you the double faults from a practice match I played the day after I did that serve practice. I had a few aces and a lot of unreturned 1st serves as well as some unreturned 2nd serves. I even through in some of the kick serves down the T that worked well.
Unfortunately I had way too many double faults as well.
I put them all together to see if there’s anything additional I should work on when practicing. I know in my practice and in the match it looks like my contact point is wrong.