Hi @remie,
I have posted a related question 9 days ago and get some response … so they are already “alerted”
If I use
https://packages.atlassian.com/mvn/maven-external/
(with a slash at the end), instead of a 404 I get redirected to
https://repo1.maven.org/maven2/
The other URL, https://packages.atlassian.com/mvn/maven-atlassian-all/, is redirected to https://maven.artifacts.atlassian.com with the error message you provided.