Seems to depend on the country. I have to login to Unidays before I am able to buy anything, there are also other options like calling Apple or going to a physical store and show them a proof.
And the Unidays login from the German Apple Store gives me an error because the University is in Austria but the Austrian store does not ship to Germany. 🙁 Seems I have to wait until I am back in Austria again.
At least I don't really need anything at the moment, so it's better for my bank account anyway. 😉
Edit: But I am pretty sure I made to it the final step earlier this year, when I just wanted to try what happens.