Could not to get environment variables in clean architecture

[hanushi]

I am trying to run the project using
dotnet watch -p src/WebApi run

I got this error.

Unhandled exception. System.ArgumentNullException: String reference not set to an instance of a String. (Parameter 's')
   at System.Text.Encoding.GetBytes(String s)
   at Infrastructure.Files.AuthenticationExtension.AddTokenAuthentication(IServiceCollection services, IConfiguration config) in /src/Infrastructure/Files/AuthenticationExtension.cs:line 14
   at TechneTravel.Infrastructure.DependencyInjection.AddInfrastructure(IServiceCollection services, IConfiguration configuration) in /src/Infrastructure/DependencyInjection.cs:line 75
   at Program.<Main>$(String[] args) in /src/WebApi/Program.cs:line 21
watch : Exited with error code 134
watch : Waiting for a file to change before restarting dotnet

I guess The issue is because of not getting the values of environment values.

AuthenticationExtension.cs

    public static IServiceCollection AddTokenAuthentication(this IServiceCollection services, IConfiguration config)
    {
        var secret = config.GetSection("Tokens").GetSection("Key").Value;

        var key = Encoding.ASCII.GetBytes(secret);
      
     // removed rest
   }

This is my appsettings.Development.json

  {
"Tokens": {
    "Key": "my-token",
    "Issuer": "issuer",
    "Audience": "audience",
    "ExpirationInMinutes": 1440
  },
// removed rest
}