403 Forbidden on API request

[Cornel Punga]

Hello,

I am writing a Lua client for VT and when sending a file to scan the response is:
HTTP/1.1 403 Forbidden
[server] => Google Frontend
[content-type] => text/html; charset=utf-8
[connection] => close
[date] => Sat, 02 Apr 2016 18:02:53 GMT
[content-length] => 0
[cache-control] => no-cache

Here is the code that sends the request .
Can somebody explain why this situation happens and what can be the problem?

Thank you!

* I supposed that other programmers who wrote a VT client may have encountered such a problem.