Hi @PeterK , I want to help you with this question.
I tried to recreate the error and I could imagine that you forgot to assign the reader permissions on the specific automation account resource for the service principal (app registration).
I will get the same error when I forget this.
Otherwise, the Postman request works. My test automation account had no jobs but I got an empty array back.
If the reply was helpful, please don’t forget to upvote or accept it as an answer, thank you.