ESP8266 Webserver not responding to C# WebRequest for temperature data via Wi-Fi

Hi. I am working with a colleague in a team project and we are to make a communication via wi-fi with a flat control device. At the very beginning I would like to read the temperature from this system. I am in charge of writing the control application my colleague is in charge of the control system. My problem is that I cannot connect via the C# application to this server.
Arduino code
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C# code

After uploading to the Arduino that a friend lent me, the port monitor displays me something like this




In the browser I can see the result



However, my application throws an exception


I searched a bit on this topic and found a solution on the electrode
https://www.elektroda.pl/rtvforum/topic3076767.html

However, I don't know how to set this page header in this arduino webserver and that's why I'm writing this post. Could someone help me with this problem ?
Thank you in advance.

Wouldn't it be simpler to do it over UDP?

I don't know. I got this code and this is how I'm trying to connect. I'm not familiar with Arduino at all and would like to fiddle with something. For me, the best option would be to control it with JSONs sent. Is it possible to do something like this over UDP? Can you give me a concrete example? Thanks in advance