not working in Docker Proxy of Nexus repository

I’m trying to configure Nexus with a Docker Proxy for to proxy the gitlab-runner-helper image ( - but an error appears in the Nexus log:

anonymous - Failed to retrieve docker bearer token
2023-05-25 15:25:00,394+0200 WARN  [qtp702342186-465944]  anonymous org.apache.http.impl.auth.HttpAuthenticator - BEARER [complete=true] authentication error: Could not retrieve token from Status code: 403

I can pull the image without a proxy, but this one seems to fail. What am I missing?

My cross post from the Nexus forum: Docker Proxy for not working - Sonatype Nexus Repository - Sonatype Community