My .csproj
code for below Azure Functions Test Case in checking the breaking changes for the NewtonSoft.Json
NuGet Package:
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<TargetFramework>net6.0</TargetFramework>
<AzureFunctionsVersion>v4</AzureFunctionsVersion>
</PropertyGroup>
<ItemGroup>
<PackageReference Include="Microsoft.NET.Sdk.Functions" Version="4.1.3" />
<PackageReference Include="Newtonsoft.Json" Version="13.0.2" />
</ItemGroup>
<ItemGroup>
<None Update="host.json">
<CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
</None>
<None Update="local.settings.json">
<CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
<CopyToPublishDirectory>Never</CopyToPublishDirectory>
</None>
</ItemGroup>
</Project>
- Check if your
Newtonsoft.Json
NuGet Package version is compatible with the .NET version and Azure Functions Core Tools version.
- The Same issue registered in SO 62853320 and resolved by the user @ThiagoCustodio like downgrading the Version of that NuGet Package and check the version compatibility with the other dependencies used in the Function Code.
Following these MS Doc1 & Doc2, Created a Sample code snippet to test any breaking changes in that NuGet Pakcage with the .NET 6 Azure Functions:
using System;
using System.IO;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.Http;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;
using Newtonsoft.Json;
namespace KrishNet6FunAppAWJTest
{
public class Account
{
public string Name { get; set; }
public string Email { get; set; }
public DateTime DOB { get; set; }
}
public static class Function1
{
[FunctionName("Function1")]
public static async Task<IActionResult> Run(
[HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = null)] HttpRequest req,
ILogger log)
{
log.LogInformation("C# HTTP trigger function processed a request.");
Account account = new Account
{
Name = "John Doe",
Email = "john@nuget.org",
DOB = new DateTime(1980, 2, 20, 0, 0, 0, DateTimeKind.Utc),
};
string json = JsonConvert.SerializeObject(account, Formatting.Indented);
Console.WriteLine(json);
string responseMessage = "Hello Krishna, This HTTP triggered function executed successfully.";
return new OkObjectResult(responseMessage);
}
}
}

Checked with the latest version of the NuGet Package Newtonsoft.Json
with the Azure Functions .NET 6 Core with the sample code snippet and working successfully and check by downgrading the NuGet Package Version along with all other Code, Dependencies Versions Compatibility.