Curl to VB.Net Visual basic

I am trying to take a Curl example and make it work from within VB.Net using Visual Basic in VS 2022 Community. I have tried everything that I can think of to make this work, but everything returns 400 (Bad Request). My first thoughts concerned the "data" of the request. The target site's example has this:

curl --location '/v2/Upload/FilesBase64' \
--header 'Content-Type: application/json' \
--data '{
  "transmitter": {
    "username": "",
    "password": ""
  },
  "simulateUpload": true,
  "files": [
    {
      "fileName": "TEST_dummy1.txt",
      "ContentType": "text/plain",
      "fileContentBase64": "ZHVtbXk="
    }
  ]
}'

Which I duplicated with the following code in VB:

'Get the file content
Dim FileData As String() = {IO.File.ReadAllText(FullFileName)}
Dim byt As Byte() = System.Text.Encoding.UTF8.GetBytes(FileData(0))
Dim Content As String = Convert.ToBase64String(byt)

'Build the body of the request
Dim Dta As New Dictionary(Of Object, Object)
Dim Transmitter As New Dictionary(Of Object, Object) From {
    {"username", USR},
    {"password", PWD}
}

Dta.Add("trasnmitter", Transmitter)
Dta.Add("simulateUpload", True)

Dim FileListarray As New List(Of Object) From {
    New Dictionary(Of Object, Object) From {
        {"filename", "TEST_DataFile.txt"},
        {"ContentType", "text/plain"},
        {"filecontentbase64", Content}
    }
}

Dta.Add("files", FileListarray.ToArray)
Dim Body As String = JsonConvert.SerializeObject(Dta, Formatting.Indented)
Dim BodyBytes As Byte() = Encoding.UTF8.GetBytes(Body)

Which produced the following (formatted here for clarity):

{
    "trasnmitter": {
      "username": "xxxxxxx",
      "password": "xxxxxxx"
    },
    "simulateUpload": true,
    "files": [
      {
        "filename": "TEST_DataFile.txt",
        "ContentType": "text/plain",
        "filecontentbase64": "MUYgICAg=="
      }
    ]
}

Lastly, I use this code to sent and retrieve the response:

Dim BodyBytes As Byte() = Encoding.UTF8.GetBytes(Body)

'build the web request
Dim URL As String = BaseURL & "/v2/Upload/FilesBase64"
Dim WebRequest As Net.WebRequest = WebRequest.Create(URL)
WebRequest.ContentType = "application/json"
WebRequest.Method = "POST"
WebRequest.ContentLength = Body.Length

'transmit the request
Dim Stream As Stream = WebRequest.GetRequestStream()
Stream.Write(BodyBytes, 0, Body.Length)
Stream.Close()

'get the response
Dim ServerText As String = ""
Try
    Dim Response As WebResponse = WebRequest.GetResponse
    Dim ResponseStream As New StreamReader(Response.GetResponseStream)
    ServerText = ResponseStream.ReadToEnd
Catch ex As Exception
    Dim ttt = ""
End Try

Please note, this is still highly in development, and I haven't expanded the error handling. If anyone has any ideas on what is wrong, please let me know!

JSON is case-sensitive. Your JSON differs from the sample JSON in its case.

Your ContentLength is also wrong, should be BodyBytes.Length, not Body.Length, in both the assignment of WebRequest.ContentLength and the call to Stream.Write.

Unrelated to your question, but you should be Using the request and response streams.