Wow, that was easy! You have been most helpful and its much appreciated. I am only a few months into this and completely new to servers. This community has been unbelievably great and extremely helpful.Sure is, you need to use the internal hostnames and ports. See:
Linking Apps Internally | TrueCharts
You'll often need to connect individual apps to each other to exchange data, for example: Sonarr to SABnzbd to allow Sonarr to control downloads within SABnzbd.truecharts.org