Amazon just set digital comics back three years. They bought Comixology, the largest digital comics reseller and service, a while back and although Amazon has a decent track record pertaining acquisitions and their ongoing existence, this is one they botched right away.
You used to be able to buy comics from within the Comixology app, via an in-app purchase. Simple and effective, because this meant you opened the app just to see if there was something interesting to read. Tap, comic bought, and start reading right away.
Now you can’t do that anymore.