Create Parallel Tests with 3rd party cloud host in C#

Has anyone tried this with Browserstack I am unable to perform it after looking through the documentation.
I created an app.config:

I created a Parallels class
class iParallel
protected IOSDriver _IOSdriver;
[TestFixture(“parallel”, “iPhone XR”)]
[TestFixture(“parallel”, “iPhone 11”)]
//[TestFixture(“parallel”, “iPhone 8”)]

    public class ParallelTest : BrowserStackNUnitTest

        public ParallelTest(string profile, string device) : base(profile, device) { }

I have a BrowserstackNUnitTest class and use: AppiumOptions opt = new AppiumOptions();

        foreach (string key in caps.AllKeys)
            opt.AddAdditionalCapability(key, caps[key]);

            foreach (string key in devices.AllKeys)
            opt.AddAdditionalCapability(key, devices[key]);

            String username = Environment.GetEnvironmentVariable("BROWSERSTACK_USERNAME");
            if (username == null)
                username = ConfigurationManager.AppSettings.Get("user");

            String accesskey = Environment.GetEnvironmentVariable("BROWSERSTACK_ACCESS_KEY");
            if (accesskey == null)
                accesskey = ConfigurationManager.AppSettings.Get("key");

        opt.AddAdditionalCapability("browserstack.user", username);
        opt.AddAdditionalCapability("browserstack.key", accesskey);

            String appId = Environment.GetEnvironmentVariable("BROWSERSTACK_APP_ID");
            if (appId != null)
            opt.AddAdditionalCapability("app", appId);
        // _IOSdriver = new IOSDriver<IOSElement>(new Uri("http://" + ConfigurationManager.AppSettings.Get("server") + "/wd/hub/"), capability);
        Uri uri = new Uri("http://" + ConfigurationManager.AppSettings.Get("server") + "/wd/hub/");
           _IOSdriver = new IOSDriver<IOSElement>(uri, opt);

When running this I get System.nullReferenceException: object reference not set to an instance of an object.