

If you have a ComiXology Unlimited subscription (which you also have to sign up for in a web browser), you can download any comics with the Unlimited banner across their covers from within the app.

Make your purchases there, and you'll find them waiting for you in the "My Books" section of the ComiXology app next time you open it. The Safari app on your iOS device will work just fine. To purchase the items you want to buy, you'll need to visit in a web browser. What you can do in the app is flag any comics you want to purchase by adding them to your wishlist. See It Downloading ComiXology Comics on iPhone and iPadPresumably due to Apple's rule about taking 30% of in-app purchases on iOS, ComiXology doesn't let you buy comics from within the app on iPhone or iPad.
