Thanks Lucas, the issue was the Object Ownership settings had ACLs disabled. All works now.
Separately, after the render the “Public URL” won’t show in make. I can see that the “CDN Link” is working with the video going into my S3 bucket in the Renders list of Shotstack, but the url won’t populate in make.com with all the other fields data. Also tried removing the S3 destination and the shotstack hosting url won’t come through either. The Render Link (Private URL) will show but not the “Public link”. Is this a sandbox limitation?