Metadata is automatically generated in NXRM by the artifact you upload. How it is driven differs by format but you don’t add it via NXRM, you add it via the artifacts you are putting in NXRM.
I suspect that probably doesn’t help very much but I also suspect your question is about the format rather than NXRM.
Folks still may be able to help you here if you provide more info on what you need.
Some formats, such as NPM support custom attributes but NXRM itself doesn’t have a custom metadata feature. Tagging is going to be the closest option right now. You can create a tag (maybe give it the same name as the artifact you want to tag), then attach that tag to an artifact or artifacts. Those tags will then be visible in the UI when looking at artifact details as well as through the rest API. The next release will have a new tag search field allowing you to search for artifacts assigned to individual tags as well.
That curl command worked for me (after changing the IP address). What version of Nexus Repository Manager are you running?
You can do that using the Tag Attributes as you have in your example. The next step is to associate your newly created tag and attributes to the components to which you would like to attach the metadata. See this section of the docs: Tagging - Associate Components with a Tag
I run version 3 (OSS 3.13.0-01), I recently downloaded and installed, I have a trial license for Nexus Firewall which will expire in two days.
I run Nexus in a VM, it works fine, apart from the tagging api.
Following up on your Trial License. I have made our Account Team aware of your request so that they can help resolve any questions around the License and help guide you through your evaluation.