Using Sonatype Nexus as RPM Proxy

Hi,

i try to use Sonatype Nexus Repository Manger for my offline server to get packages. I've used the explaination from sonatype

https://help.sonatype.com/repomanager3/nexus-repository-administration/formats/yum-repositories/proxying-rhel-yum-repositories
to get it running, but it don't work. I don't understand how the mechanism of the yum/dnf redhat plugin works. i've registerd the server with the ceretificates i've downloaded.

i still get access denied from cdn.redhat.com on the nexus repository srever

the nexus server is running on cent os 7

has somebody already done this before?