What you're doing wrong is assuming that the Amdatu repositories are Maven repositories. They are not. They are in fact OSGi Bundle Repositories, and we provide an index in both the "old" (repository.xml) and "new" (index.xml) format.
Within the Amdatu project, we don't use Maven, we develop with Bndtools, so you would have to provide the proper metadata (pom.xml) yourself and then import the bundles into your own Maven repository. If someone would contribute a tool to automatically generate the proper metadata and/or upload artifacts in Maven central, we would be happy to accept that though.