API in . NET Core - api does not find connection string from appsettings.json

Question

I did all the development on a windows machine but after almost a week I was able to deploy on a Ubuntu 18.04 machine and set the settings to access via https.

But now I came across the following error when I need to connect to the bank.

Argumentnullexception: Value cannot be null. (Parameter 'connectionString')

Before the server and ssl related changes the connection string was coming with the value but now it comes null

My Program.Cs

public class Program ( a parte com mais mudanças para o deploy)
{
    public static void Main(string[] args)
    {
       var host = new WebHostBuilder()
        .UseContentRoot(Directory.GetCurrentDirectory())
        .UseUrls("https://*:5001;http://*:5000", "http://*:80")
        .UseKestrel(options =>
              {
                  options.ListenAnyIP(443, listenOptions =>
                  {
                      listenOptions.UseHttps("chave.pfx", "senha");
                  });
              })
        .UseStartup<Startup>()
        .Build();

        host.Run();
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
     Host.CreateDefaultBuilder(args)
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            });
}

In appsettings.json I create the string

     {
      "DbContextSettings": {
        "ConnectionString": "Host=host;Port=port;Pooling=true;Database=Banco;User Id=postgres;Password=******;"
      },
    }

In Startup.Cs I try to retrieve the string but here it is not getting the connection there from appsettings

   public Startup(IHostingEnvironment env)
        {
            var builder = new ConfigurationBuilder()
                .SetBasePath(env.ContentRootPath)
                .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
                .AddEnvironmentVariables();
            Configuration = builder.Build();
        }    
    public void ConfigureServices(IServiceCollection services)
      {
         ...
         var connectionString = Configuration["DbContextSettings:ConnectionString"];
         services.AddDbContext<APIMeuContexto>(opts => opts.UseNpgsql(connectionString));
         ...
       }

I’d like to understand why appsettings is no longer being seen by the startup (since before the deployment api worked) and how to fix it. I imagine now he might be looking for appsettings.json somewhere else. But I don’t know how to figure that out.