I am making a call to an API I am developing and I get an error: JsonTypeInfo metadata for type ‘BFNG_Library.Models.App_admin’ was not provided by TypeInfoResolver of type ‘[]’.

This is the class. And I added the JsonSerializable attribute:

public record App_admin
{
    public string? Role { get; set; }
    public string? Name { get; set; }
    public string? Email { get; set; }
    public int? ID { get; set; }
    public bool? Active { get; set; }
}

[JsonSerializable(typeof(App_admin))]
[JsonSerializable(typeof(List<App_admin>))]
internal partial class AppJsonSerializerContext2 : JsonSerializerContext
{

}

and this is the API endpoint in my controller:

 public class AdminController : Controller
 {
     [Route("api/admin/create")]
     public string PostCreate([FromBody] App_admin Admin)
     {
         //Implementation Removed
     }
}

Not sure if it makes a difference, but the class (App_admin) is in a different project (BFNG_Library) which I have added as a project dependency on the actual project (BFNG_Program).

I even changed the API signature to require a string instead of App_admin viz:

 public string PostCreate([FromBody] string Admin)

When I do this, the error changes to JsonTypeInfo metadata for type ‘System.String’ was not provided by TypeInfoResolver of type ‘[]’.

I find it quite confusing as String is a base type. Is there some missing config I have not included?

Environment:
Windows, .Net 8

Any help will be appreciated