Trouble posting json using httpwebrequest in VB.NET

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I'm working on a project to get a client's data via a vb.net watcher program to a web service. I didn't write the web side or the API for it. I have access to those developers but I'm stuck on something they are not versed in. I've tested my json in jsonlint and it's perfect. My connection code is fine too. I've tested that using a test API they created. There's something else going on that I'm missing. I'm getting a "bad request" error when I run their upload data API. No details. That's all it's returning to me. They've successfully tested it on their end using a different front end but I'm doing my part in vb.net.

Edit: I should note that when I use one of the API's they provide to pull data OUT of their system, that works fine. I can retrieve what I need. In that case I don't need the lines that deal with passing the json block (the GetRequestStream related stuff). I must be doing something wrong with respect to that.

Edit (2019-03-01): Note that I had found some variations on my code and tried them as well, such as what's shown here. There are other similar strategies that claim to work. I could not get that strategy to work either. I'm getting the same error as the person who posted that ticket.

What I have tried:

Here's my code:

Dim hwReq As HttpWebRequest = Nothing
Dim hwResp As HttpWebResponse = Nothing

Try

    Dim noticeDataBodyContentBytes As Byte() = System.Text.Encoding.Unicode.GetBytes(noticeDataBodyContent)

    hwReq = HttpWebRequest.CreateHttp(webPortalURI)
    hwReq.Method = "POST"
    hwReq.ContentType = "application/json; charset=unicode"
    hwReq.ContentLength = noticeDataBodyContentBytes.Length
    hwReq.Accept = "application/json"
    hwReq.Headers.Add("timestamp", ts)
    hwReq.Headers.Add("apiclient", My.Settings.WebPortalClientID)
    hwReq.Headers.Add("apitoken", atkn)

    Dim noticeDataBodyContentStream As Stream = hwReq.GetRequestStream()
    noticeDataBodyContentStream.Write(noticeDataBodyContentBytes, 0, noticeDataBodyContentBytes.Length)
    noticeDataBodyContentStream.Close()

    hwResp = CType(hwReq.GetResponse, HttpWebResponse) '<<<<< error is here


Catch ex As Exception
    xfrmMain.memWatcherActivity.Text = "ERROR (" & DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss") & "): " & friendlyErrorMessage & " - see log file for more info" & vbCrLf & xfrmMain.memWatcherActivity.Text
    errorMessageToLog = "ERROR: " & friendlyErrorMessage & " - " & ex.Message & vbCrLf & ex.StackTrace & vbCrLf & "(" & MethodBase.GetCurrentMethod().ReflectedType.FullName & ".vb." & MethodBase.GetCurrentMethod().Name & ")"
    Utilities.LogToFile(errorMessageToLog)
    If My.Settings.DevMode Then
        MessageBox.Show(errorMessageToLog, Application.ProductName, MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
    Else
        SendEmailMessage("ERROR: " & friendlyErrorMessage, errorMessageToLog, emergencyEmailPersonsArray)
    End If

Finally
    If hwResp IsNot Nothing Then
        hwResp.Close()
        hwResp.Dispose()
        hwResp = Nothing
    End If
    hwReq = Nothing

End Try

I don't get a response when the error occurs. It jumps to my exception handler.

My json block is in the noticeDataBodyContent variable. Like I said, I tested the json in jsonlint and it's perfect.

Hoping someone can let me know what I'm doing wrong here.

Thanks in advance!

Keith

Edit (2019-03-01): I changed my strategy to HttpClient and I got a little further. Instead of the above, I'm doing this now:

Dim hc As New HttpClient
hc.DefaultRequestHeaders.Add("timestamp", ts)
hc.DefaultRequestHeaders.Add("apiclient", My.Settings.WebPortalClientID)
hc.DefaultRequestHeaders.Add("apitoken", atkn)
Dim u As New Uri(webPortalURI)
Dim sc As New StringContent(noticeDataBodyContent, Encoding.UTF8, "application/json")
Dim resp = hc.PostAsync(u, sc)
resp.Wait()

This is what I get back now:

{StatusCode: 400, ReasonPhrase: 'Bad Request', Version: 1.1, Content: System.Net.Http.StreamContent, Headers:
{
Vary: Accept-Encoding
Vary: origin
Vary: accept-encoding
Cache-Control: no-cache
Date: Fri, 01 Mar 2019 14:17:50 GMT
Server: nginx/1.15.8
Content-Length: 65
Content-Type: application/json; charset=utf-8
}}