Publishing Scala library to a Sonatype Nexus repository

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I'm trying to publish a Scala library to a self-hosted Sonatype Nexus repository. I'm using Mill 1.0.6.

Following docs at https://mill-build.org/mill/scalalib/publishing.html#_non_staging_releases_classic_maven_uploads results in

Cannot resolve external module mill.scalalib.publish.SonatypePublisher

I've also tried following https://mill-build.org/mill/scalalib/publishing.html#_publishing_2 and get:

Cannot resolve external module mill.scalalib.MavenPublishModule.

What am I doing wrong?