Преобразование почтового запроса C++ API в код Delphi

Я программирую в Delphi, и мне трудно преобразовать запрос C++ API POST в delphi. Я пытался использовать Indy, как и раньше, с предыдущими API, но этот, похоже, не работает с тем, что я пытаюсь. Может ли кто-нибудь помочь мне с этим?

Код С++, который мне нужно преобразовать:

CURL *hnd = curl_easy_init();

curl_easy_setopt(hnd, CURLOPT_CUSTOMREQUEST, "POST");
curl_easy_setopt(hnd, CURLOPT_URL, "https://sandbox.checkbook.io/v3/check/digital");

struct curl_slist *headers = NULL;
headers = curl_slist_append(headers, "accept: application/json");
headers = curl_slist_append(headers, "content-type: application/json");
headers = curl_slist_append(headers, "Authorization: xxxxxxxxxxxxxxxx:xxxxxxxxxxxxxxxxx");
curl_easy_setopt(hnd, CURLOPT_HTTPHEADER, headers);

curl_easy_setopt(hnd, CURLOPT_POSTFIELDS, "{\"recipient\":\"[email protected]\",\"name\":\"Widgets Inc.\",\"amount\":5,\"description\":\"Test Payment\"}");

CURLcode ret = curl_easy_perform(hnd);

Код Delphi, который у меня есть:

unit API_InvoiceCloud;

interface

uses
  DB, SysUtils,  System.Classes, System.JSON, IdSSLOpenSSL, VCL.Dialogs,
  IdHTTP, XML.XMLIntf, xml.xmlDom, xml.XMLDoc, IDCoder, IDCoderMIME,
  IdBaseComponent, IdException{, IdZLibCompressorBase{, IdCompressorZLib{,Rest.Client};

procedure CreateDigitalPayment_CheckBookAPI(mRecipientEmailAddress,
                                      mRecipientName : String;
                                      mPaymentAmount : Double;
                                      mPaymentNumber,
                                      mPaymentDescription : String);


implementation

var
  { INDY COMPONENT TO CONNECT TO API SERVER; MAKES CONNECTION }
  IDHTTP1 : TidHttp;
  { SSL Connection }
  SSL : TIdSSLIOHandlerSocketOpenSSL;
  { Request and Response vars }
  JsonRequest, InJson : String;
  JsonToSend : TStringStream;    //object to store json text and pass API
  JObj : TJSONObject;
Const
  { Constant variables holding the APIKEY+APISECRET and BASEURL }
  nBASEURL = 'https://sandbox.checkbook.io/v3/check/digital';
  nAPIKEY = 'xxxxxxxxx:xxxxxxxx';

procedure CreateDigitalPayment_CheckBookAPI(mRecipientEmailAddress,
                                            mRecipientName : String;
                                            mPaymentAmount : Double;
                                            mPaymentNumber,
                                            mPaymentDescription : String);
var
  { Response into String }
  SinglePartyResponse : String;
  ResponseCode : String;  
  { -----------Testing---------- }
  //lParamList: TStringList;
  nBASEURL : String;
  RequestBody : TStream;
  ResponseBody : String;
begin
  
  { JSON body with request string }
  JsonRequest := '{"recipient":"' + mRecipientEmailAddress
                + '","name":"' + mRecipientName
                + '","amount":' + FloatToStr(mPaymentAmount)
                + ',"number":"' + mPaymentNumber
                + '","description":"' + mPaymentDescription + '"}';
  
  try

    try
      { Create connection instance }
      IDHTTP1 := TidHttp.Create;

      { SSL Configuration }
      SSL := TIdSSLIOHandlerSocketOpenSSL.Create;
      SSL.SSLOptions.SSLVersions := [sslvTLSv1_1, sslvTLSv1_2];
      IDHTTP1.IOHandler := SSL;

      { Headers/Params }
      IDHTTP1.Request.Clear;
      IDHTTP1.Request.CustomHeaders.FoldLines := False;
      IDHTTP1.Request.Accept := 'application/json';
      IDHTTP1.Request.ContentType := 'application/json';
      IDHTTP1.Request.CustomHeaders.Values['Authorization'] := nAPIKEY;
      
      { Saving JSON text to TStringStream Object }
      JsonToSend := TStringStream.Create(JsonRequest, TEncoding.UTF8);
      //JsonToSend := TStringStream.Create(JsonRequest, TEncoding.ASCII);

      { Making POST Request using INDYs TidHTTP component; Params are: URL, JsonStringObj - saving into variable }
      SinglePartyResponse := IDHTTP1.Post(nBASEURL, JsonToSend);
      
      ShowMessage(IDHTTP1.ResponseCode.ToString);

    except
      on E : Exception do
        { Display error message if cannot do API CALL }
        begin
          ShowMessage(E.ClassName+' error raised, with message : "' + E.Message + '".');
          Abort;
        end
    end;

  finally
    { Free objects from memory }
    IDHTTP1.Free;
    SSL.Free;
    JsonToSend.Free;
  end;
  
end;

end.

Когда я пытаюсь сделать запрос POST, я получаю ошибку 400 Bad Request. Я не уверен, что я делаю неправильно здесь.