borg2 non-AWS s3 repo example anyone?

[tve]

I'm trying to test borg2 on Hetzner, i.e. S3 compatible but for the life of me I can't figure out how to do a repo-create:

./borg-2.0.0b20 -r s3:hetz@https://nbg1.your-objectstorage.com/borg-test/v2.0.0b20 repo-create -e repokey-blake2-chacha20-poly1305
Error: Invalid or unsupported Backend Storage URL: s3:hetz@https://nbg1.your-objectstorage.com/borg-test/v2.0.0b20

I have a ~/.aws/credentials file with something like:

[hetz]
aws_access_key_id=XRM........
aws_secret_access_key=PR1.......

I tried passing the access key and secret in the URL but that didn't go any better. Are there some examples somewhere I can adapt?