OAuth 2.0 Authorization Code flow grant type - PQ API Connection

Hi, i'm tryng to to get Access Token from an OAuth2 Authorization Code flow.

Here the code: "PART 1" work fine and return the Authorization Code, bat "PART 2" don't work and return error.

Thanks for help

let

// PART 1: Get Authorization Code
Body = 
"{
""username"":""<MyUsername>"",
""password"":""<MyPsw>"",
""scope"":[""<SelectedScope>""]
}",

url = "http://XXXXXXXXXXXXXXXXXXXXXXXXXXX/api/login/sso",
GetJson = Json.Document(Web.Contents(url, [Headers=[ContentType="application/json"], Content=Text.ToBinary(Body)])),
AuthorizationCode = GetJson,

// The previous code correctly returns the Authorization Code

// PART 2: Now I try to Get Access Token passing the Authorization Code, the client_id and the client_secret

// Base64 Encoding
a = "<client_id>" & ":" & "<client_secret>",
a2 = Text.ToBinary(a),
a3 = Binary.ToText(a2, BinaryEncoding.Base64),

TokenURL = "http://XXXXXXXXXXXXXXXXXXXXXXXXXXX/oauth2/token/",
Body2 = 
"{
""grant_type"": ""authorization_code"",
""code"": """&AuthorizationCode&""" 
}",

Source = Web.Contents(TokenURL, [Headers = [ContentType="application/json", Authorization = "Basic "&a3&""], Content = Text.ToBinary(Body2)])

in Source