Took me a while to figure out that a user in Matillion cannot run a job that writes to s3 (apparently) without being designated as an "Admin" in the User Configuration area. Didn't realize this was the case, so spun wheels on it a bit. I thought that the AWS service account was what Matillion was using across users.
I assumed that the "Admin" designation had more to do with the administration of the Matillion instance, but I assume this is a security measure of some sort?
In any case, addition to the help info that makes this clear would be helpful. If I'm missing something, please let me know.