Thank you for your approaches @Troon
Sometimes it’s helpful just to write to someone. I have just been able to solve the problem - it was probably a problem with the authentication.
multiscrape:
- name: Wallbox
resource: https://192.168.2.36/cgi_s_ldp1.session
scan_interval: 60
verify_ssl: false
form_submit:
submit_once: True
resource: https://192.168.2.36/
select: "form"
input:
username: admin
password: "xxxxxx"
sensor:
- unique_id: Zaehlerstand
name: Wallbox Zählerstand
select: "tr:nth-child(20) > td:nth-child(2)"
Here are a few more keywords in case someone else has the same problem and would like to include their Compleo / Innogy Wallbox professional Pro in Home Assistant over the LAN connected webinterface.