diff --git a/python_ifirma/core.py b/python_ifirma/core.py
index f441797..5699009 100644
--- a/python_ifirma/core.py
+++ b/python_ifirma/core.py
@@ -3,8 +3,8 @@ import json
 import datetime
 from time import strftime
 
+from python_ifirma.exceptions import PythonIfirmaExceptionFactory
 from python_ifirma.helpers import Helpers
-
 import requests
 
 
@@ -67,7 +67,7 @@ class Position:
         }
 
 
-class Invoice:
+class NewInvoiceParams:
     def __init__(self, client, positions):
         self.client = client
         self.positions = positions
@@ -115,6 +115,20 @@ class iFirmaAPI():
         self.__invoice_key_value = Helpers.unhex_key_value(_invoice_key_value)
         self.__user_key_value = Helpers.unhex_key_value(_user_key_value)
 
+    @staticmethod
+    def __execute_post_request(headers, request_content, url):
+        response = requests.post(url, data=request_content, headers=headers)
+        response_dict = json.loads(response.content.decode("utf-8"), 'utf-8')
+        if "response" not in response_dict:
+            raise PythonIfirmaExceptionFactory.throw_exception_by_code(-1)
+        real_response_content = response_dict["response"]
+        response_code = real_response_content.get("Kod", -1)
+
+        if response_code != 0:
+            raise PythonIfirmaExceptionFactory.throw_exception_by_code(response_code)
+
+        return response_dict
+
     def __create_invoice_and_return_id(self, invoice, url):
         request_content = json.dumps(invoice.get_request_data(), separators=(',', ':'))
         request_hash_text = "{}{}{}{}".format(
@@ -131,8 +145,9 @@ class iFirmaAPI():
                 Helpers.get_hmac_of_text(self.__invoice_key_value, request_hash_text)
             )
         }
-        response = requests.post(url, data=request_content, headers=headers)
-        response_dict = json.loads(response.content.decode("utf-8"), 'utf-8')
+
+        response_dict = self.__execute_post_request(headers, request_content, url)
+
         if response_dict["response"].get("Identyfikator"):
             invoice_id = response_dict["response"]["Identyfikator"]
             return invoice_id
diff --git a/python_ifirma/exceptions.py b/python_ifirma/exceptions.py
new file mode 100644
index 0000000..1c7b6a8
--- /dev/null
+++ b/python_ifirma/exceptions.py
@@ -0,0 +1,25 @@
+class PythonIfirmaExceptionFactory:
+    @staticmethod
+    def throw_exception_by_code(code):
+        if code == 201:
+            raise BadRequestParameters()
+        elif code == 400:
+            raise BadRequestStructureException()
+        raise UnknownException()
+
+
+class PythonIfirmaException(BaseException):
+    code = None
+
+
+class UnknownException(PythonIfirmaException):
+    code = -1
+
+
+class BadRequestParameters(PythonIfirmaException):
+    code = 201
+
+
+class BadRequestStructureException(PythonIfirmaException):
+    code = 400
+
diff --git a/python_ifirma/tests.py b/python_ifirma/tests.py
index 020b7dc..13d0507 100644
--- a/python_ifirma/tests.py
+++ b/python_ifirma/tests.py
@@ -1,6 +1,7 @@
 from unittest.case import TestCase
 
-from python_ifirma.core import Client, iFirmaAPI, Invoice, Position, VAT, Address
+from python_ifirma.core import Client, iFirmaAPI, NewInvoiceParams, Position, VAT, Address
+from python_ifirma import exceptions
 from python_ifirma.helpers import Helpers
 
 
@@ -92,7 +93,6 @@ class TestClient(TestCase):
 
 class TestCreateInvoice(TestCase):
     def setUp(self):
-        print("SERUP")
         self.ifirma_client = iFirmaAPI(TEST_IFIRMA_USER, TEST_IFIRMA_INVOICE_KEY, TEST_IFIRMA_USER_KEY)
 
         self.client = Client(
@@ -105,11 +105,12 @@ class TestCreateInvoice(TestCase):
         self.position = Position(VAT.VAT_23, 1, 1000, "nazwa", "szt")
 
     def test_generate_invoice(self):
-        invoice = Invoice(self.client, [self.position])
+        invoice = NewInvoiceParams(self.client, [self.position])
         self.assertIsNotNone(self.ifirma_client.generate_invoice(invoice))
 
     def test_generate_invoice_with_position_with_bad_vat(self):
         bad_position = Position(0.22, 1, 1000, "nazwa", "szt")
 
-        invoice = Invoice(self.client, [bad_position])
-        self.assertIsNone(self.ifirma_client.generate_invoice(invoice))
\ No newline at end of file
+        with self.assertRaises(exceptions.BadRequestParameters):
+            invoice = NewInvoiceParams(self.client, [bad_position])
+            self.ifirma_client.generate_invoice(invoice)
\ No newline at end of file