Have either of you used any other discount from UNiDAYS before? Testing your UNiDAYS accounts out with other deals would be super-helpful to narrow the problem down.
@HobunPang - have you tried using the discount with any other Spotify login details at all? Is it just your Facebook details you've been using to login? Does anyone else have access to your UNiDAYS login details - if so, is it possible they've used your UNiDAYS account for their own Spotify discount? You'd likely get an "already used discount" message if that was the case.
Sorry for the delay here. I should've noticed before but @Ondrej and @TaliaBergaglio - your accounts are German and Italian respectively. The UNiDAYS discount is only open to UK students at the moment I'm afraid. But if everything goes well with it, hopefully we'll be able to extend it in the future.
I too am receiving the same error that says "the student id is invalid". Also i'm a UK student and unidays has worked well for me with other sites. For the past month Ive changed my subscription from UK to Singapore spotify. However now that i'm back in the uk, I've been attempting to re subscribe to the UK unidays spotify deal, but it hasnt been successful.