TL:DR
Why do so shitty "API"s exist that are even harder to write than proper ones? D:

Trying to hack my venilation at home.
This API is so horrible D:
The API is only based on POST requests no matter if you want to write values or get values and the response only contains XML with cryptic values like:

<?xml version="1.0" encoding="UTF-8"?>
<PARAMETER>
<LANG>de</LANG>
<ID>v01306</ID>
<VA>00011100000000000000000010000001</VA>
<ID>v00024</ID>
<VA>0</VA>
<ID>v00033</ID>
<VA>2</VA>
<ID>v00037</ID>
<VA>0</VA>

Also there are multiple API routes like
POST /data/werte1.xml
POST /data/werte2.xml
POST /data/werte3.xml
POST /data/werte4.xml
And actually the real API route is only given in the request body and not in the path.

Why is this so shitty? D:<

Btw in terms of security this is also top notch. It just globally saves if one computer sends the login password.
I mean why even ask for a password then? D:
That made me end up with a cronjob to send a login request so I don't have to login on any device.

PS:
You see, great piece of German engineering.