Why is the request sent incorrectly?

Question

API

Why is the response coming through the browser and not through telnet? I tried to write my own client (it doesn’t work in C, yes in python, but I need it in C), but does it return the same thing there?

Answer 1

I started writing a comment about almost 20 years of http/1.1 existence, but everything is a bit simpler:
https://tools.ietf.org/html/rfc2616#section-14.23
You grossly violated the standard. You presented yourself as an HTTP/1.1 client, but did not pass the Host header required by this standard.
Incorrect client request is code 400, the server answers you correctly.
The minimum possible request for HTTP/1.1 is two lines:

GET /... HTTP/1.1
Host: api.vk.com

Some more headers may be required, but this is already necessary. Browsers typically send a lot of extra headers.
One line was allowed a long time ago for HTTP/1.0, where there could be a maximum of 1 site per IP. Most modern servers will listen to you over HTTP/1.0 but are unlikely to return what you want, because they will not know which domain you are asking about and, accordingly, to which handler to transfer the request.

Answer 2

Your request is missing the required headers. Make out request as it is necessary on the standard instead of stupidly GET in one line.