Unable to play Smooth Stream

Hi All -

New AWS user here...
I followed the "Video on Demand on AWS Foundation" reference solution to transcode mp4 into HLS, DASH, and Smooth Stream output formats. I set up a Cloudfront distribution as well and configured it for Smooth Streaming as per AWS docs (https://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/on-demand-video.html), made everything public, set up CORS etc.

However, I'm still not able to play my Smooth Streaming content (HLS and DASH are fine). I tested the output video with the Microsoft test server and ExoPlayer on my streaming stick. Both players try to load the content, progress bar indicates the correct duration, but no video or audio.

Exoplayer log: "com.google.android.exoplayer2.upstream.HttpDataSource$InvalidResponseCodeException: Response code: 400"
If I try to play publicly available Smooth streams like: https://test.playready.microsoft.com/smoothstreaming/SSWSS720H264/SuperSpeedway_720.ism/manifest, Exoplayer successfully plays the stream.

So, I'm guessing there's something I didn't set up properly with my MediaConvert/CloudFront setup

My Media Convert job:
input: one mp4 (1920 x 1080, avc) -> two MS Smooth outputs (1280 x 720 and 640 x 360) avc

Does anyone have pointers on how to root cause this?

Thanks.