Remote Repository Access with username and password

Hi Forum!

I'm trying to access a repository which is secured with username and password via nexus. I've configured the repository as a proxy repository and set the username and password in the configuration at "Authentication (optional)" but this is not working.
I can access the remote repository directly with the browser and with maven but not through nexus. What could be wrong?

I hope someone could help me.

Best regards.
csc