I have added a local Sonatype Docker Registry to my Teamcity instance. When adding the Connection, testing the login succeeds and returns,
Connection to https://nexus.octopusdemos.app/repository/nexus-docker/v2/ was successful!
When using the connection in a build definition and attempting to push to this registry, I receive
Cannot login to registry nexus.octopusdemos.app/repository/nexus-docker
An error occurred while executing 'docker login -u "******" --password-stdin nexus.octopusdemos.app/repository/nexus-docker':
Error response from daemon: login attempt to https://nexus.octopusdemos.app/v2/ failed with status: 404 Not Found
The error is valid, that URL doesn't exist, but that's not the URL it was configured with.