I thought I had followed all the steps correctly but clearly something isn't right. This probably boils down to my understanding of DNS and nameservers because I am still new to this stuff. I'm good at developing apps but still weak in this area.
Anyway, I'm getting the CDN not returning HTTP Challenge and I'm not sure what else I can do. Please review my screenshots and let me know if you see where the problem is!
I am using Heroku's ACM.