diff --git a/.gitignore b/.gitignore
index b98a174..a1a8580 100644
--- a/.gitignore
+++ b/.gitignore
@@ -294,3 +294,5 @@ $RECYCLE.BIN/
 # Windows shortcuts
 *.lnk
 
+# Sensitive details
+config.yaml
diff --git a/app/data/invoices.csv b/app/data/invoices.csv
index 6d7aba2..32e76ac 100644
--- a/app/data/invoices.csv
+++ b/app/data/invoices.csv
@@ -1,2 +1,2 @@
 Rechnungsnummer;Email;Anrede
-RE357891;isaak.buslovich@trocknerheld.de;Isaak Trocknerheld
+RE255111;fws-rs@vielhuber.eu;Sehr geehrter Herr Vielhuber
diff --git a/app/lexoffice.py b/app/lexoffice.py
new file mode 100644
index 0000000..3d22a0c
--- /dev/null
+++ b/app/lexoffice.py
@@ -0,0 +1,58 @@
+"""
+Module: lexoffice.py
+Description: Provides an interface to interact with the Lexoffice API.
+This module enables operations such as retrieving invoice details from Lexoffice,
+making it easier to integrate Lexoffice API functionality into a Flask application.
+"""
+
+from pathlib import Path
+import yaml
+import requests
+import logging
+
+
+class LexofficeAPI:
+    """Class to handle interactions with the Lexoffice API."""
+
+    def __init__(self):
+        """Initialize with the Lexoffice API access token from a config file."""
+        self.base_url = "https://api.lexoffice.io/v1"
+        self.headers = {
+            "Authorization": f"Bearer {self._load_api_token()}",
+            "Content-Type": "application/json",
+            "Accept": "application/json"
+        }
+
+    @staticmethod
+    def _load_api_token() -> str:
+        """Load the API token from the config.yaml file."""
+        config_path = Path(__file__).parent.parent / 'config.yaml'
+        with config_path.open('r') as file:
+            config = yaml.safe_load(file)
+        return config['lexoffice']['api_token']
+
+    def get_invoice_total_gross_amount(self, invoice_id: str) -> float:
+        """
+        Retrieve the total gross amount for a specific invoice.
+
+        Args:
+            invoice_id (str): Unique identifier of the invoice.
+
+        Returns:
+            float or None: Total gross amount of the invoice, or None if an error occurs.
+        """
+        url = f"{self.base_url}/invoices/{invoice_id}"
+
+        try:
+            response = requests.get(url, headers=self.headers)
+            response.raise_for_status()
+            return response.json().get('totalPrice', {}).get('totalGrossAmount')
+
+        except requests.exceptions.RequestException as e:
+            logging.error(f"Error fetching invoice: {e}")
+            return None
+
+# Usage example:
+# lexoffice_api = LexofficeAPI()
+# total_gross_amount = lexoffice_api.get_invoice_total_gross_amount('your_invoice_id')
+# print(total_gross_amount)
diff --git a/app/routes.py b/app/routes.py
index ff794a7..4da4e89 100644
--- a/app/routes.py
+++ b/app/routes.py
@@ -1,8 +1,10 @@
 from flask import render_template, redirect, url_for, current_app, render_template_string, request
 import os
 import csv
-
 from app import app, htmx
+import logging
+
+from app.lexoffice import LexofficeAPI
 
 
 def read_invoices_from_csv(csv_file_path):
@@ -10,10 +12,11 @@ def read_invoices_from_csv(csv_file_path):
         with open(csv_file_path, mode='r', encoding='utf-8') as file:
             return list(csv.DictReader(file, delimiter=';'))
     except FileNotFoundError:
-        current_app.logger.error(f"CSV file not found at {csv_file_path}")
+        logging.error(f"CSV file not found at {csv_file_path}")
+        return []
     except csv.Error as e:
-        current_app.logger.error(f"Error reading CSV file: {e}")
-    return []
+        logging.error(f"Error reading CSV file: {e}")
+        return []
 
 
 @app.route('/load-invoices')
@@ -48,31 +51,46 @@ def buchhaltung():
 @app.route('/add-invoice', methods=['POST'])
 def add_invoice():
     csv_file_path = os.path.join(current_app.root_path, 'data', 'invoices.csv')
+
+    # Extract invoice data from form
     new_invoice = {
         'Rechnungsnummer': request.form['rechnungsnummer'],
         'Email': request.form['email'],
-        'Anrede': request.form['anrede']
+        'Anrede': request.form['anrede'],
+        # Initialize 'Betrag' with a placeholder (to be updated)
+        'Betrag': 'N/A'
     }
 
     try:
-        # Read the existing data
+        # Fetch the total gross amount for the new invoice using LexofficeAPI
+        lexoffice_api = LexofficeAPI('your_access_token')  # Replace with actual access token
+        total_gross_amount = lexoffice_api.get_invoice_total_gross_amount(new_invoice['Rechnungsnummer'])
+
+        # Update 'Betrag' in the new invoice data
+        if total_gross_amount is not None:
+            new_invoice['Betrag'] = total_gross_amount
+
+        # Read existing data from CSV
         with open(csv_file_path, 'r', newline='', encoding='utf-8') as csvfile:
             reader = csv.DictReader(csvfile, delimiter=';')
             fieldnames = reader.fieldnames
+            if 'Betrag' not in fieldnames:
+                fieldnames.append('Betrag')
             existing_data = list(reader)
 
         # Add the new invoice at the beginning of the data
         existing_data.insert(0, new_invoice)
 
-        # Write the updated data back to the file
+        # Write the updated data back to the CSV file
         with open(csv_file_path, 'w', newline='', encoding='utf-8') as csvfile:
             writer = csv.DictWriter(csvfile, fieldnames=fieldnames, delimiter=';')
             writer.writeheader()
             writer.writerows(existing_data)
 
         return redirect(url_for('buchhaltung'))
+
     except Exception as e:
-        current_app.logger.error(f"Error updating CSV file: {e}")
+        logging.error(f"Error updating CSV file: {e}")
         return "An error occurred while adding the invoice", 500
 
 
diff --git a/app/static/css/style.css b/app/static/css/style.css
index b5af572..186760f 100644
--- a/app/static/css/style.css
+++ b/app/static/css/style.css
@@ -1,5 +1,5 @@
 /* Import Google Fonts */
-@import url('https://fonts.googleapis.com/css2?family=Roboto:wght@400;700&display=swap');
+@import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;700&display=swap');
 
 /* Root and Variable Definitions */
 :root {
@@ -17,7 +17,7 @@
 
 /* Body and Global Styles */
 body {
-    font-family: 'Roboto', sans-serif;
+    font-family: 'Inter', sans-serif;
     margin: 0;
     padding: 0;
     background: var(--light-grey);
diff --git a/app/templates/partials/invoice_table.html b/app/templates/partials/invoice_table.html
index 673e891..c691328 100644
--- a/app/templates/partials/invoice_table.html
+++ b/app/templates/partials/invoice_table.html
@@ -5,6 +5,7 @@
                 <th>Rechnungsnummer</th>
                 <th>Email</th>
                 <th>Anrede</th>
+                <th>Betrag</th>
             </tr>
         </thead>
         <tbody>
@@ -13,6 +14,7 @@
                 <td>{{ invoice['Rechnungsnummer'] }}</td>
                 <td>{{ invoice['Email'] }}</td>
                 <td>{{ invoice['Anrede'] }}</td>
+                <td>{{ invoice['Betrag'] }}</td>
             </tr>
             {% endfor %}
         </tbody>
diff --git a/requirements.txt b/requirements.txt
index 1431bc6..2812aa6 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1 +1,3 @@
 flask~=2.2.5
+requests~=2.25.1
+pyyaml~=6.0.1
diff --git a/run.py b/run.py
index 2d5f0ce..7ed3731 100644
--- a/run.py
+++ b/run.py
@@ -1,4 +1,7 @@
+import logging
 from app import app
 
 if __name__ == '__main__':
+    logging.basicConfig(filename='app.log', level=logging.DEBUG,
+                        format='%(asctime)s %(levelname)s %(name)s : %(message)s')
     app.run(debug=True)