F# webpage Authentication - authentication

Question

I've been trying to authenticate the bitstamp api however, I keep on getting the following error:
"{\"error\": \"Missing key, signature and nonce parameters\"}"
The code I have written to do this is below:
let nounce = System.DateTime.Today.Ticks
let hexdigest (bytes : byte[]) =
let sb = System.Text.StringBuilder()
bytes |> Array.iter (fun b -> b.ToString("X2") |> sb.Append |> ignore)
string sb
let signature =
use hmac = new HMACSHA256(System.Text.Encoding.ASCII.GetBytes(stampsecret))
hmac.ComputeHash(mes)
|> hexdigest
I am calling the website with the following:
let ordersBTCbuy()=
Http.Request("https://www.bitstamp.net/api/buy", meth="Post", query=["key", stampkey; "signature", signature.ToLower(); "nonce", string(nounce); "amount", "1"; "price", string(convertB)])
A reference to the API can be found here: https://www.bitstamp.net/api/
Update I've changed the web address to:
let ordersBTCbuy()=
Http.Request("https://www.bitstamp.net/api/buy/", meth="Post", query=["key", stampkey; "signature", signature.ToLower(); "nonce", string(nounce); "amount", "1"; "price", string(convertB)])
My new issue is now the signature my representation is 64 characters long and upper case however I still seem to have an error.

Answer 1

When creating a POST request. Your key-value pairs need to go in the body.
To do that using FSharp data do the following:
let postBody = FormValues([ "key", stampkey; "signature", signature.ToLower(); "nonce", string(nounce); "amount", "1"; "price", string(convertB)])
let ordersBTCbuy()=
Http.Request("https://www.bitstamp.net/api/buy", httpMethod="Post", body=postBody)