diff --git a/setup.py b/setup.py
index 463856d..c00dc03 100644
--- a/setup.py
+++ b/setup.py
@@ -2,7 +2,7 @@ from setuptools import setup, find_namespace_packages
 
 setup(
     name='superfaktura_client',
-    version='0.0.1',
+    version='0.0.2',
     packages=find_namespace_packages(),
     url='https://github.com/eledio-helpers/superfaktura-client',
     license='',
diff --git a/superfaktura/superfaktura_api.py b/superfaktura/superfaktura_api.py
index 789b156..09d059b 100644
--- a/superfaktura/superfaktura_api.py
+++ b/superfaktura/superfaktura_api.py
@@ -8,6 +8,9 @@ from dotenv import load_dotenv  # type: ignore
 class SuperFakturaAPIException(Exception):
     pass
 
+class SuperFakturaAPIMissingCredentialsException(Exception):
+    pass
+
 
 class SuperFakturaAPI:
     def __init__(self) -> None:
@@ -16,6 +19,9 @@ class SuperFakturaAPI:
         self._api_url = os.getenv("SUPERFAKTURA_API_URL")
         _api_mail = os.getenv("SUPERFAKTURA_API_EMAIL")
         _api_company_id = os.getenv("SUPERFAKTURA_API_COMPANY_ID")
+        if not _api_key or not self._api_url or not _api_mail or not _api_company_id:
+            raise SuperFakturaAPIMissingCredentialsException('Please ensure, that necessary credentials are set. Please see README.md')
+
         self._auth_header = {
             "Authorization": f"SFAPI email={_api_mail}&apikey={_api_key}&company_id={_api_company_id}"
         }