It isn't that hard ^.^
When we enter to register, we can see that it asks for invite-code..
Let's see the source:
Uhmm.. This one seems interesting, when we enter it we get:
I'll use jsbeautifier.org:
So, there are two functions, one to check, and to generate!
we'll focus on the generate one..
So it creates a request of type POST to: https://www.hackthebox.gr/api/invite/generate
With this in Postfields: dataType=json
Awesome, let's try to send a request like that and see the result..
We got code!
let's decode that base64
And here we go, we got our registration code
Hope it helped, if you got stuck in the registration of course!