Hi @andy222,
Very sorry for the frustrations here - it's frustrating for all of us too (me especially) when it doesn't work 
Just to give some context here --- we made a huge investment in BuildMaster 2022/23, and one of the areas was a major improvement for how we integrate with ProGet. The feed::FeedName and directory::AssetDirName convention is brand new, and it's an improvement/simplification on the "Secure Resource" convention that you discovered. However, both conventions -- as well as directly specifying those values on the operation -- are still supported. There's a lot (too much?) flexibility.
Unfortunately this particular scenario / use case (downloading assets from ProGet) was simply not one that we focused on:
- Uploading assets is uncommon, but still happen
- Downloading assets is rare... and not something I've seen done in BuildMaster much
NuGet packages are not uncommon when coming from TeamCity/Octopus model. Regardless, we didn't focus on this use case. We felt most new users are seeking Git, .NET, Maven, Build, CI Import, and Docker, so that's where most of our effort was focused..
That said.... I would love to make your scenario / use case something really easy to set-up, so hopefully that will give you the confidence to continue!
In this case, it's a "trivial problem" where something just didn't get "wired" up the right way. I can clearly see from the code that the ApiUrl parameter is not being wired-up as it should be.
We'll get this fixed ASAP, just an extension fix. We just need to set up the scenario and make sure it works on our end first.
Cheers,
Alex