maven: does not download extension written by myself - maven

Question

I am not so deep into maven but had to write an extension.
I successfully deployed and it is present.
https://www.simuline.eu/RepositoryMaven/eu/simuline/qMngmnt/0.0.3/
Also the version fits.
But nevertheless, when trying to use,
Unresolvable build extension: Plugin eu.simuline:qMngmnt:0.0.3 or one of its dependencies could not be resolved:
eu.simuline:qMngmnt:jar:0.0.3 was not found in https://repo.maven.apache.org/maven2 during a previous attempt. This failure was cached in the local repository and resolution is not reattempted until the update interval of central has elapsed or updates are forced
In my pom i have:
<repositories>
<repository>
<id>publicRepoAtSimuline</id>
<name>repo at simuline</name>
<url>https://www.simuline.eu/RepositoryMaven</url>
</repository>
</repositories>
and I use it at the following places:
<build>
<extensions>
<extension>
<groupId>eu.simuline</groupId>
<artifactId>qMngmnt</artifactId>
<version>0.0.3</version>
</extension>
...
<plugins>
...
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-checkstyle-plugin</artifactId>
<version>3.1.2</version>
<dependencies>
<dependency>
<groupId>com.puppycrawl.tools</groupId>
<artifactId>checkstyle</artifactId>
<!-- 8.15 has security issue ans seemingly line lengths are wrong -->
<version>10.1</version><!-- TBD: make 8.30, 9.1, 10.1 work -->
</dependency>
<dependency>
<groupId>eu.simuline</groupId>
<artifactId>qMngmnt</artifactId>
<version>0.0.3</version>
</dependency>
</dependencies>
...
<dependencies>
<dependency><!-- TBD: clarify: for spotbugs: necessary? -->
<groupId>eu.simuline</groupId>
<artifactId>qMngmnt</artifactId>
<version>0.0.3</version>
<!--scope>provided</scope-->
</dependency>
Interesting: if i build a new version, qMngmnt-0.0.4-SNAPSHOT
then of course it is locally installed, and all works fine.
So I have the impression, download never worked but i did not realize so far.
What is wrong?
By the way: I use another artifact as an artifact item
but neither as a dependency nor as an extension and it works just fine.