code: private Map<String, String> buildPayload(String jsonPayload) {
          Map<String, String> params = new HashMap<String, String>();
          params.put("api_key", apiKey);
          params.put("format", handler.getSailthruResponseHandler().getFormat());
          params.put("json", jsonPayload);
          params.put("sig", getSignatureHash(params));
          return params;
      }
docs: Build HTTP Request Payload
  @param jsonPayload JSON payload
  @return Map Object