Getting Error

at RestSharp.HttpRequestMessageExtensions.g__AddHeader|0_2(Parameter parameter, HttpHeaders httpHeaders)
at RestSharp.HttpRequestMessageExtensions.c__DisplayClass0_0.b__1(Parameter x)
at RestSharp.Extensions.CollectionExtensions.ForEach[T](IEnumerable1 items, Action1 action)
at RestSharp.HttpRequestMessageExtensions.AddHeaders(HttpRequestMessage message, RequestHeaders headers)
at RestSharp.RestClient.d__5.MoveNext()
at RestSharp.RestClient.d__1.MoveNext()
at RestSharp.AsyncHelpers.c__DisplayClass1_01.b__0>d.MoveNext() at RestSharp.AsyncHelpers.CustomSynchronizationContext.g__PostCallback|7_0>d.MoveNext() at RestSharp.AsyncHelpers.CustomSynchronizationContext.Run() at RestSharp.AsyncHelpers.RunSync(Func1 task)
at RestSharp.AsyncHelpers.RunSync[T](Func`1 task)
at RestSharp.RestClientExtensions.Execute(IRestClient client, RestRequest request)

Code Snippet:

RestRequest request = GetRequestObject(alertNotificationTransfer);
RetryPolicy policy = Policy.HandleResult(x => x.StatusCode != HttpStatusCode.Created)
.WaitAndRetry(myRetryCount, retryAttempt => TimeSpan.FromSeconds(myWaitIntervalInSeconds));
var response = policy.Execute(() => myRestClient.Execute(request));
//...

internal RestRequest GetRequestObject(NotificationTransfer alertNotificationTransfer)
{
    var request = new RestRequest(GetEnvironmentVariable(myRelativeUrlKey), Method.Post);
    request.RequestFormat = DataFormat.Json;
    request.AddJsonBody(alertNotificationTransfer);
    return request;
}

I made changes in my code to RestResponse earlier it was IRestResponse as IRestResponse is depricated in latest version.