C# Webclient Post to AWS API Gateway Endpoint - amazon-web-services

Question

I am having some problems attempting to post to an API gateway endpoint.
On my API gateway I have my gateway all set up, and tested via the tool and am getting results and can verify that the step function is in fact executing the request appropriately.
{
"executionArn": "arn:aws:states:us-east-2:xxxxxxxxxxxx:execution:DevStateMachine-XXXXXXXXXXX:c9047982-e7f8-4b72-98d3-281db0eb4c30",
"startDate": 1531170720.489
}
I have set up a Stage for this for my dev environment and all looks good there as well. where I am given a URL to post against.
https://xxxxxxxxxx.execute-api.us-east-2.amazonaws.com/dev/assignments
In my c# code I have the web client defined as follows:
public Guid QueueAssignment(AssignmentDTO assignment)
{
using (var client = new HttpClient())
{
var data = JsonConvert.SerializeObject(assignment);
var content = new StringContent(data);
var uri = "https://xxxxxxxxxx.execute-api.us-east-2.amazonaws.com/dev/assignments"
content.Headers.ContentType = new MediaTypeHeaderValue("application/json");
var response = client.PostAsync(uri, content).Result;
if (response.IsSuccessStatusCode)
{
_logger.Info("Successfully posted to AWS Step Function");
_logger.Info(response);
}
else
_logger.Error("Error posting to AWS Step Function");
_logger.Error(response);
}
}
Everytime this post is attempted I get the following error:
System.Net.WebException: The remote name could not be resolved: 'https://xxxxxxxxxx.execute-api.us-east-2.amazonaws.com'
Is there something I am missing in posting to this URI or some type of conversion I need to do? Im kind of at a loss on where to go on this on.