I found the documentation somewhat confusing.

> Give the bucket a name and attach the sample policy from "My Billing Dashboard" > Preferences.

The first step in configuring the S3 bucket refers to something that's explained in more detail in the second step. Feels like the order of thing is off.

Using cross account access rewarded me with a validation error without helpful instructions. I followed the common issues without luck. I think that's a problem.

Key based access worked for me at the first attempt. However, it's not immediately clear you have to give PowerUser and ReadOnly rights like in the first section.

Good luck with the further development of your product!