When I learnt AppSync it was from The Burning Monk ( Yan Cui ) and his AppSync Masterclass.
I've spoken with him and you can get any of his courses at a massive 15% discount using code "swilliams15".
https://theburningmonk.thinkific.com/courses
Buy any of the courses and just make sure to use the code "swilliams15" at checkout for 15% discount.
* If you use my code then you get a discount and I also get an affiliate kickback.