Hi Candy Ng
I was able to replicate this issue with owner roles while testing from content safety studio
Here is the solution.
1.Role assignment
Could you add your email address as "Cognitive Services User" from "Add Role Assignment" from IAM of your content safety resources.
Post adding above roles, I am able to get result.
Attached screenshot after adding above role.
2. Correct directory and resource
Also, make sure that you are in correct working directory and selected your resources
Reference - https://learn.microsoft.com/en-us/azure/ai-services/content-safety/overview#security
Hope it helps.
Thank you.