Nexus mirror (with maven) does not work

Im using Nexus as mirror for maven central and want to add other repositories. If I add this like this

   <repositories>
        <!-- org.spigotmc.spigot-api -->
        <repository>
            <id>papermc</id>
            <url>https://papermc.io/repo/repository/maven-public/</url>
        </repository>    
        <!-- co.aikar.acf-paper -->
        <repository>
            <id>aikar</id>
            <url>https://repo.aikar.co/content/groups/aikar/</url>
        </repository>
    </repositories>

to my pom.yml with the following in the settings.xml

  <mirrors>
    <mirror>
      <id>dio-maven-registry</id>
      <url>${MAVEN_REPO_URL}</url>
      <mirrorOf>central</mirrorOf>
    </mirror>
  </mirrors>

I can build my Jar. Now I add the repositories each as a Nexus proxy to the central group. I use the same URLs and replace central with *. The proxy the settings are the like for the central proxy, but I can not access the maven packages:

[WARNING] 
[WARNING] Some problems were encountered while building the effective model for io.digon.xpaper:xcore:jar:1.0.0-SNAPSHOT
[WARNING] 'build.plugins.plugin.version' for org.apache.maven.plugins:maven-deploy-plugin is missing. @ line 80, column 17
[WARNING] 
[WARNING] It is highly recommended to fix these problems because they threaten the stability of your build.
[WARNING] 
[WARNING] For this reason, future Maven versions might no longer support building such malformed projects.
[WARNING] 
[WARNING] The POM for com.destroystokyo.paper:paper-api:jar:1.16.5-R0.1-SNAPSHOT is missing, no dependency information available
[WARNING] The POM for co.aikar:acf-paper:jar:0.5.0-SNAPSHOT is missing, no dependency information available
[ERROR] Failed to execute goal on project XX: Could not resolve dependencies for project XX.XX.XX:XX:jar:1.0.0-SNAPSHOT: The following artifacts could not be resolved: com.destroystokyo.paper:paper-api:jar:1.16.5-R0.1-SNAPSHOT, co.aikar:acf-paper:jar:0.5.0-SNAPSHOT: Could not find artifact com.destroystokyo.paper:paper-api:jar:1.16.5-R0.1-SNAPSHOT in dio-maven-registry (XXXX) -> [Help 1]

Can someone give me a hint after hours of searching around ... Greetings, Kokos Bot.