[Solved] Unable to load the service index for source https://nuget.telerik.com/v3/index.json.

[Jerry]

Using VS2026.

When I clone our project and then try to build it, I get this error:

Unable to load the service index for source https://nuget.telerik.com/v3/index.json. 
Response status code does not indicate success: 401 (Unauthorized).
 
In the "tools -> nuget package manager -> package manager settings -> nuget package manager -> configuration files", I see several nuget.config files.
The first nuget.config in the list is in located in the solution folder.
The second nuget.config in located in the "users\myname\AppData\roaming\nuget\" folder
The second nuget.config contains my nuget.telerik UID and PW. The first nuget.config does not have that info. Not sure if this matters or if I can switch the priority.
Also, I tried downloading my "telerik-license.txt" and placed it in my solution folder. Did not help.
Online it says to add source "https://nuget.telerik.com/v3/index.json" and use telerik UI and PW. Unsure where to do this.
I also removed then added the "Sources" through the VS2026 UI "nuget package manager -> sources", shown here. But I was never asked for a UID and PW as the articles online say would happen.
nuget.org	https://api.nuget.org/v3/index.json
TelerikOnlineFeed	https://nuget.telerik.com/v3/index.json
 
Also, when I open this solution in VS2026, a dialog appears asking to update "Telerik UI for ASP.NET Core version update". 
"Version Update" -> "Please, log in to download the latest version of Telerik UI for ASP.Net Core"
When I click the button, a web page appears saying I was successfully logged into telerik. When I return to VS2026, there is an error:
"Authentication did not succeed. Please try again"
 
How can I resolve this?
 

[Lance | Senior Manager Technical Support]

Hi Jerry,

Thank you for the information thus far. Let me separate the relevant topics so you can approach this logically.

Package Sources

Yes, dotnet will load all the package sources defined from both nuget config files:

• the global one in your roaming folder (%appdata%/NuGet/NuGet.Config)
• and the one in your project/solution directory

So, I suspect what is happening is the source defined in one of them has matching credentials somewhere, but the other one does not.

The trick to avoid dotnet from using your global one is to add a <clear /> line in your project-specific one, just prior to its package sources. Here's a real-world example from my DevOpsExampels repo => src/NuGet.Config#L14 

Once you have control over the package sources that Visual Studio and dotnet is using, let's move onto credentials.

Package Source Credentials

Look at what the package source's name is in your config file, do you have a matching packageSourceCredentials for it? See my screenshot above again, the name in my example is "Telerik_v3_Feed" so that source needs either:

• Option 1 - a matching credential in the config file, like my screenshot
• or
• Option 2 - it can be set in the command line with the dotnet nuget source update command.

I personally like to use Option #1 in a shared repo because it is predictable and only needs environment variables in the target environment (works everywhere, on every OS)

Let's continue with that example I shared, it has this variable placeholder syntax

    <Telerik_v3_Feed>
      <add key="Username" value="%TELERIK_USERNAME%" />
      <add key="ClearTextPassword" value="%TELERIK_PASSWORD%" />
    </Telerik_v3_Feed>

Local Dev PC

On your local PC, all you need is to set two local user environment variables:

• Key: TELERIK_USERNAME
• Value "api-key" (yes, that literal string value)

and

• Key: TELERIK_PASSWORD
• Value: the API key I generated on https://www.telerik.com/account/downloads/api-keys 

Like this:

CI-CD

I know you're not asking for any information about CI here, but I thought I could add it fully explain the benefit of having those variable placeholders.

Now, for any GitHub Actions or Azure DevOps, you can easily set the vars with a pipeline secret:

- name: Restore NuGet packages
  run: dotnet restore MyApp.csproj
  env:
    TELERIK_USERNAME: "api-key"
    TELERIK_PASSWORD: ${{secrets.TELERIK_API_KEY}}

License Key File

This topic is unrelated to the NuGet server credentials. That telerik-license.txt file just need to sit in your roaming folder for license activation when you compile your code.

1. Open your %appdata%/telerik/ folder
2. Make sure the telerik-license.txt file is present in that directory

We will automatically find that file and use it when you project gets compiled

Further Assistance

If you need to dig deeper and share more information that you don't want to be in the forums, please consider opening a technical support ticket instead. This will be a private conversation and doesn't need to be in the public community forums as it is specific to your implementation.

[EDIT 1] Added screenshot of the Windows user Environment Variables editor to clarify.