Unexpected error occurred on a receive using API on my Wix site - vb.net

Question

I've made an experimental email and password system using post requests to my Wix site API and I've verified it works through curl and postman. When trying to use it in my VB.NET app however I get the error: "The underlying connection was closed: An unexpected error occurred on a receive." I already previously ran into a "Could not create SSL/TLS secure channel" error but that was resolved when I moved the .NET framework for the project to 4.7.1 and made sure SecurityProtocol was set to SystemDefault as Wix seems to use TLS 1.3. Now however I'm getting this error on receive that I have no idea how to resolve as everything in the request seems to look ok:
ServicePointManager.SecurityProtocol = SecurityProtocolType.SystemDefault
Dim req As HttpWebRequest = DirectCast(WebRequest.Create(New Uri("https://xxxxx.com/mysite/_functions/check?email=" & email & "&pass=" & LCase(passHash))), HttpWebRequest)
req.Method = "POST"
req.ContentType = "none"
req.ContentLength = 0
req.Host = "test"
req.KeepAlive = True
Dim result As HttpWebResponse = req.GetResponse()
The error is thrown when running 'req.GetReponse()'.
After looking at countless versions of sample code for .NET POST requests and questions about this error but everyone seems to suggest setting the security prococol type, which I have done and setting it as the system default is the only way I don't get an internal server error status. Another was setting KeepAlive to false, which I have also tried but didn't make any difference.
What could be the problem here? Here is what's included in the postman header if this is of help:

Answer 1

Ok so eventually I ended up changing my code to use GetResponseAsync() instead of GetResponse() (not that it made any difference to the problem) and set the protocol type back to Tls12 on .NET 4.8. In the end it seemed that having req.Host set was what was causing the issue with the response, Wix doesn't seem to like it. I also added some extra settings to the request but ultimately they make no difference to the response. Here is the final working code:
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12
Dim req As HttpWebRequest = WebRequest.CreateHttp("https://example.com/check?email=" & email & "&pass=" & LCase(passHash))
req.Method = "POST"
req.ContentType = "none"
req.ContentLength = 0
req.KeepAlive = True
req.CookieContainer = New CookieContainer()
req.UserAgent = "Test"
req.Accept = "ext/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8"
req.Headers.Add(HttpRequestHeader.AcceptLanguage, "en-US;q=0.9,en;q=0.5")
req.Headers.Add(HttpRequestHeader.AcceptEncoding, "gzip, deflate;q=0.8")
req.Headers.Add(HttpRequestHeader.CacheControl, "no-cache")
Dim statusCode As HttpStatusCode = Nothing
Try
Using result As HttpWebResponse = CType(Await req.GetResponseAsync(), HttpWebResponse)
statusCode = result.StatusCode
End Using
If statusCode = HttpStatusCode.OK Then
MsgBox("Valid")
Else
Dim response As String = New StreamReader(req.GetResponse().GetResponseStream()).ReadToEnd()
MsgBox(response)
End If
Catch webEx As WebException
MsgBox(New StreamReader(webEx.Response.GetResponseStream()).ReadToEnd())
End Try