Connect via openssl
openssl s_client -connect okboomer.tasteless.eu:10401

Send GET request
GET / HTTP/1.1
Host: okboomer.tasteless.eu

In the Header:
Flag: `tstlss{always keep looking}`

Note: This was not visible in the developer console or with python requests. This was because it was a trailing header. Trailing headers are sent after the content with a zero length chunk.