Self-hosted runner artifact upload FAILED with error AccessDenied

I’m running some benchmarks on a self-hosted runner, butI can’t upload the results. Is there any configuration I have missed or wrong here that is preventing artifact upload from working ?

- store_artifacts: # store the benchmark output
path: tmp/benchmark-results

FAILED with error AccessDenied: Access Denied
status code: 403, request id: …

Or is this likely to be a network configuration issue ? I’m on an EC2 instance which was prepared for me.