Entity Framework Core Migrations reading connection from appsettings.json

I'm having issues reading a connection string from an appsettings.json file.

I'm using a .netstandard2.0 .dll in which I have EfCore packages and Configuration

The sln structure is as following.

I have an webApi , an EfCore.dll and some DI.dll that resolves all dependencies.

When running in the package manager console (from EfCore assembly)

Add-Migration Name

I have the following error

Value cannot be null.

Parameter name: connectionString

This is the class that I've implemented in order for Migrations to work. following this article https://docs.microsoft.com/en-us/ef/core/miscellaneous/cli/dbcontext-creation

public class StoreContextFactory : IDesignTimeDbContextFactory<StoreContext>
    {
        IConfiguration Configuration = new ConfigurationBuilder()
              .SetBasePath(Directory.GetCurrentDirectory())
              .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
              .Build();

        public StoreContext CreateDbContext(string[] args)
        {
            var optionsBuilder = new DbContextOptionsBuilder<StoreContext>();
            optionsBuilder.UseSqlServer(Configuration["ConnectionString:SqlConnection"]);

            return new StoreContext(optionsBuilder.Options);
        }
    }

In appsettings.json I have the

 "ConnectionString": {
    "SqlConnection": "connection"
  }

When instead of Configuration["ConnectionString:SqlConnection"] I use the connection it works but when using the Configuration extension class it fails.

Any solution?

Thanks