I did this a long time ago, and for reasons that doesn't matter right now, I need to do it again on November 2022. And I realized that I forgot some important steps (some "tricks" actually) which made me spent some precious time.
So, for my own reference, but mainly and most important: for the reference of all the futures generations that you walk on the surface of this planet, here is the straight forward steps in order to have NZBGet installed correctly in a FreeBSD or TrueNAS Jail (which is my case, by the way).