The type or namespace name 'UniRx' could not be found (are you missing a using directive or an assembly reference?) code example

Example 1: The type or namespace name 'IEnumerator' could not be found (are you missing a using directive or an assembly reference?)

using System.Collections;

Example 2: The type or namespace name 'MovieContext' could not be found (are you missing a using directive or an assembly reference?)

if (Environment.IsDevelopment())
        {
            services.AddDbContext(options =>
            options.UseSqlite(
                Configuration.GetConnectionString("MovieContext")));
        }
       else
        {
            services.AddDbContext(options =>
            options.UseSqlServer(
                Configuration.GetConnectionString("MovieContext")));
        }