Azure .Net Build with JFrog Artifactory Fails

Question

I'm trying to build a WPF .Net 8 app in Azure and I need 3rd party assemblies to be hosted on JFrogs artifactory. I get this pipeline Nuget issue:

NuGet Config files used: D:\a\1\s\app\NuGet.Config

Feeds used: C:\Program Files\dotnet\library-packs https://api.nuget.org/v3/index.json https://xxx.jfrog.io/artifactory/api/nuget/v3/external-nuget-libs/index.json ##[error]The nuget command failed with exit code(1) and error(NU1301: Unable to load the service index for source https://xxx.jfrog.io/artifactory/api/nuget/v3/external-nuget-libs/index.json.

Prior to that stage I perform a successful nuget authenticate, using a Service Connection with the jfrog...index.json URL and basic authentication creds:

Setting up the credential provider for these service connections:
https://xxx.jfrog.io/artifactory/api/nuget/v3/external-nuget-libs/index.json

Finishing: NuGetAuthenticate

I can use Postman, with basic authentication, to hit the jfrog...index.json URL and it returns 200 and some json.

I followed JFrog's notes and a "nuget push" to deploy my assembly package to JFrog and a "nuget list" does list the package.

Any guidance on what I can try further to diagnose the issue is welcome.

Thanks, Steve