diff --git a/python_ifirma/core.py b/python_ifirma/core.py
index 7e91541..36cd28c 100644
--- a/python_ifirma/core.py
+++ b/python_ifirma/core.py
@@ -185,22 +185,6 @@ 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"))
-        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:
-            # print(response_code)
-            print(real_response_content)
-            raise PythonIfirmaExceptionFactory.throw_exception_by_code(response_code)
-
-        return response_dict
-
     def __get_auth_header(self, request_hash_text, key_value=""):
         key_value = key_value or self.__invoice_key_value
         return "IAPIS user={}, hmac-sha1={}".format(
@@ -223,6 +207,24 @@ class iFirmaAPI():
         response = requests.get(url, headers=headers, params=params)
         return json.loads(response.content.decode('utf-8'))
 
+    @staticmethod
+    def __post(headers, request_content, url):
+        """POST request to IFirma API"""
+
+        response = requests.post(url, data=request_content, headers=headers)
+        response_dict = json.loads(response.content.decode("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:
+            # print(response_code)
+            print(real_response_content)
+            raise PythonIfirmaExceptionFactory.throw_exception_by_code(response_code)
+
+        return response_dict
+
     def find_partner(self, keyword):
         return self.__get(f"kontrahenci/{quote(keyword)}.json",
                           self.__invoice_key_name)
@@ -241,11 +243,10 @@ class iFirmaAPI():
         headers = {
             "Accept": "application/json",
             "Content-type": "application/json; charset=UTF-8",
-            "Authentication": self.__get_auth_header(request_hash_text,
-                                                     key_value=__user_key_value)
+            "Authentication": self.__get_auth_header(request_hash_text)
         }
 
-        response_dict = self.__execute_post_request(headers, request_content, url)
+        response_dict = self.__post(headers, request_content, url)
 
         if response_dict["response"].get("Identyfikator"):
             invoice_id = response_dict["response"]["Identyfikator"]
@@ -292,7 +293,7 @@ class iFirmaAPI():
             "Authentication": self.__get_auth_header(request_hash_text)
         }
 
-        response_dict = self.__execute_post_request(headers, request_content, url)
+        response_dict = self.__post(headers, request_content, url)
 
         if response_dict["response"].get("Identyfikator"):
             invoice_id = response_dict["response"]["Identyfikator"]
@@ -308,7 +309,6 @@ class iFirmaAPI():
         return self.__get("faktury.json", self.__invoice_key_name,
                           params=params)
 
-
     def get_invoice_list(self, limit=0):
         url = "https://www.ifirma.pl/iapi/fakturaeksportuslugue/list.json"
         request_hash_text = "{}{}{}".format(