Using HTTPRequest to Obtain an Access Code

Question

I am trying to create a Mathematica equivalent to the following code:

    curl 'https://signin.tradestation.com/oauth/token' \
--request POST \
--header "Content-Type: application/x-www-form-urlencoded" \
--data 'grant_type=authorization_code' \
--data 'client_id=XXXXXXXXX' \
--data 'client_secret=XXXXXXXXX' \
--data 'redirect_uri=http://localhost' \
--data 'code=XXXXXXXXX'


curl 'https://signin.tradestation.com/oauth/token' \
--request POST \
--header "Content-Type: application/x-www-form-urlencoded" \
--data-raw 'grant_type=authorization_code&client_id=XXXXXXXXX&client_secret=XXXXXXXXX&redirect_uri=http://localhost&code=XXXXXXXXX'

My Wolfram Language code equivalent looks like this:

urlToken = "https://signin.tradestation.com/oauth/token";
headers = {"Content-Type" -> "application/x-www-form-urlencoded"};
parameters = {"grant_type" -> "authorization_code", 
   "client_id" -> apiKey, "client_secret" -> clientSecret, 
   "code" -> AuthCode, "redirect_uri" -> urlRedirect };
request = 
  HTTPRequest[
   urlToken, <|"Method" -> "POST", "Headers" -> headers, 
    "Body" -> URLQueryEncode[parameters], "VerifyPeer" -> False|>];
response = URLRead[request]

Unfortunately all this produces is:

HTTPResponse[403 Status:Forbidden]

Can anyone advise what I am doing wrong?

Is there an easier approach?