Azure Pipeline Agent can't build .NET 6 Class Library to NuGet Package

Question

I have a simple .NET 6 class library FooBarService.Contracts that contains only one DTO class FooBarRequest. I want that to be available to my team in our Azure Artifacts Feed as a NuGet package.

namespace FooBarService.Contracts.Requests;

public class FooBarRequest
{
    public string Id { get; set; }

    public FooBarRequest(string id)
    {
        Id= id;
    }
}

The azure-pipeline.yml has a stage for packing and pushing the aforementioned class library as a nuget package. I removed the irrelevant parts of the file. Update: it is the nuget push task that fails, the nuget pack task works.

pool:
  vmImage: ubuntu-latest

name: 1.0.0.0

- stage: nuget_stage
  jobs:
  - job: 'build_push_job'
    steps:
    - task: UseDotNet@2
      displayName: Use .NET 6.0
      inputs:
        packageType: 'sdk'
        version: '6.0.x'
    - task: DotNetCoreCLI@2
      inputs:
        command: 'pack'
        packagesToPack: '**/FooBarService.Contracts.csproj'
        versioningScheme: 'byBuildNumber'
    - task: DotNetCoreCLI@2
      inputs:
        command: 'push'
        packagesToPush: '$(Build.ArtifactStagingDirectory)/*.nupkg'
        nuGetFeedType: 'internal'
        publishVstsFeed: 'REDACTED_FOR_PRIVACY_REASONS/REDACTED_FOR_PRIVACY_REASONS'

All other stages are executing as planned, but this nuget_stage fails with the following error:

##[error]Error: The process '/usr/bin/dotnet' failed with exit code 1
##[error]Packages failed to publish
Info: Azure Pipelines hosted agents have been updated and now contain .Net 5.x SDK/Runtime along with the older .Net Core version which are currently lts. Unless you have locked down a SDK version for your project(s), 5.x SDK might be picked up which might have breaking behavior as compared to previous versions. You can learn more about the breaking changes here: https://docs.microsoft.com/en-us/dotnet/core/tools/ and https://docs.microsoft.com/en-us/dotnet/core/compatibility/ . To learn about more such changes and troubleshoot, refer here: https://docs.microsoft.com/en-us/azure/devops/pipelines/tasks/build/dotnet-core-cli?view=azure-devops#troubleshooting

EDIT

I added the the task with Use .NET 6.0 as suggested by @Maytham Fahmi and I'm still getting the same error.

The FooBarService.Contracts.csproj file says

<Project Sdk="Microsoft.NET.Sdk">

    <PropertyGroup>
        <TargetFramework>net6.0</TargetFramework>
        <ImplicitUsings>enable</ImplicitUsings>
        <Nullable>enable</Nullable>
        <Title>FooBarService.Contracts</Title>
        <Authors />
        <LangVersion>10</LangVersion>
    </PropertyGroup>

</Project>

Answer 1

It turns out the displayed error was not the actual cause of the failure.

Since the NuGet packing was successful, it could not have been .NET 6 causing the trouble. The NuGet pushing was the show stopper. I was distracted by the red error message at the bottom of the log and I didn't notice the subtle Response status code does not indicate success: 403 (Forbidden - User) Azure Pipeline at the beginning of the log.

The solution was to switch this project's build service role from Collaborator to Contributor as described in this Stackoverflow question.

Answer 2

you need to add this step task before all other tasks:

- task: UseDotNet@2
  displayName: Use .NET 6.0
  inputs:
    packageType: 'sdk'
    version: '6.0.x'