Why am I getting the 400 error (Bad request) - vb.net

Question

After receiving the authorization code from Google Api, I try to make a request to retrieve the user's data, but the 400 error always occurs.
Dim objSerializer = New JavaScriptSerializer()
Dim objContent = New NameValueCollection()
Dim strClientId = "****.apps.googleusercontent.com"
Dim strClientSecret = "****"
Dim strTokenUri = "https://accounts.google.com/o/oauth2/token"
Dim objClient = New WebClient()
objClient.Encoding = Encoding.UTF8
objClient.QueryString.Add("code", strCode)
objClient.QueryString.Add("client_id", strClientId)
objClient.QueryString.Add("client_secret", strClientSecret)
objClient.QueryString.Add("redirect_uri", "http://localhost:38815/Info.aspx")
objClient.QueryString.Add("grant_type", "authorization_code")
Dim data = objClient.UploadValues(strTokenUri, "POST", objClient.QueryString)
Dim objResponse As String = Encoding.UTF8.GetString(data)
Dim objGoogleJwtToken = objSerializer.Deserialize(Of GoogleAccessToken)(objResponse)
Error:
System.Net.WebException: The remote server returned an error: (400) Request Incorrect.
UPDATE
This is my post data
POST /o/oauth2/token HTTP/1.1
Host: accounts.google.com
Cache-Control: no-cache
Content-Type: application/x-www-form-urlencoded
code=4%2FewGRFvsrdTHGF698QFq6d359KAPRWc4c-8ipKjJU58X1uk14WNc5uRw45N-c88HtbWkL17wEfLlasdfGRSU&
client_id=****.apps.googleusercontent.com&
client_secret=****&
redirect_uri=http%3A%2F%2Flocalhost%3A38815%2FInfo.aspx&
grant_type=authorization_code
I receive the following json result:
{
"error": "invalid_grant",
"error_description": "Bad Request"
}

Answer 1

After some tests I found another error that is related to the following topic:
https://github.com/morgoth/picasa/issues/39
Even correcting the redirect_uri parameter was still not getting the authenticated token, so I used the Http client for .NET Restsharp and got the following solution that worked:
Private Shared Function GetAccessToken3(ByVal strCode As String, ByVal strClientId As String, ByVal strClientSecret As String, ByVal strTokenUri As String) As GoogleAccessToken
Dim objClient As RestClient
Dim objIResponse As IRestResponse
Dim objRequest As RestRequest
Dim objSerializer As New DataContractJsonSerializer(GetType(GoogleAccessToken))
Dim objResponse As GoogleAccessToken
objClient = New RestClient(strTokenUri)
objClient.Authenticator = New HttpBasicAuthenticator(strClientId, strClientSecret)
objRequest = New RestRequest(Method.POST)
objRequest.AddHeader("Content-Type", "application/x-www-form-urlencoded")
objRequest.AddHeader("Accept", "application/json")
objRequest.AddParameter("code", strCode, ParameterType.GetOrPost)
objRequest.AddParameter("client_id", strClientId, ParameterType.GetOrPost)
objRequest.AddParameter("client_secret", strClientSecret, ParameterType.GetOrPost)
objRequest.AddParameter("redirect_uri", "http://localhost:38815/Default.aspx", ParameterType.GetOrPost)
objRequest.AddParameter("grant_type", "authorization_code", ParameterType.GetOrPost)
objIResponse = objClient.Execute(objRequest)
If objIResponse.StatusCode <> HttpStatusCode.OK OrElse objIResponse.ErrorException IsNot Nothing Then
Throw New Exception("Error: " + objIResponse.StatusCode)
End If
objResponse = DirectCast(objSerializer.ReadObject(New MemoryStream(Encoding.UTF8.GetBytes(objIResponse.Content))), GoogleAccessToken)
Return objResponse
End Function
I'm validate token result in JWT Tool