I'm not sure where the problem lies, but, as I've indicated earlier, your feed url looked OK.
It should follow this format:
<CloudFront Domain>/<Feed file name>
For example,
https://d26l19cca9xspq.cloudfront.net/CuddleSaurAnimations.json
Keep in mind:
The name of the feed file is case-sensitive.
You must upload the feed file with meta-data: Content-Type application/json.
If the above does not work, it's time yo contact Roku Partner Success or Amazon for more help.
FREE Windows desktop software for converting Direct Publisher channels to SceneGraph (SDK), for creating
BIF (Trick Play) files,
Roku (MRSS, JSON) feed files, and
FireTV feed files @
GitHub/rrirower.