diff --git a/easyverein/modules/invoice.py b/easyverein/modules/invoice.py
index 853475a..338f5c3 100644
--- a/easyverein/modules/invoice.py
+++ b/easyverein/modules/invoice.py
@@ -1,8 +1,8 @@
 import logging
-from pathlib import Path
 import re
-from typing import List
 import urllib
+from pathlib import Path
+from typing import List
 
 from requests.structures import CaseInsensitiveDict
 
@@ -172,9 +172,9 @@ def get_attachment(
             )
 
         # Fix for unencoded characters - should probably be fixed in easyverein API
-        m = re.fullmatch(r'^(.*\&path=)(.*)(&storedInS3=True)$', path.unicode_string())
+        m = re.fullmatch(r"^(.*\&path=)(.*)(&storedInS3=True)$", path.unicode_string())
         url_components = list(m.groups())
-        if '%' not in url_components[1]:
+        if "%" not in url_components[1]:
             url_components[1] = urllib.parse.quote(url_components[1])
 
-        return self.c.fetch_file(''.join(url_components))
+        return self.c.fetch_file("".join(url_components))