Thanks for reaching out here and welcome to the Community! We hope you don't mind us answering in English 🙂
We'd love to help you get your Premium Student started. In order to apply for the discount, you can either log in to your college/uni's portal or upload proof of your enrollment, to verify your Student status.
If you upload proof of enrollment, you need to wait for SheerID to email you with your eligibility status. This can take a few days. When you try to reapply for the discount again, while your verification is still in process, you'll see the message that this offer has already been used.
Check your email inbox for a confirmation from SheerID to activate your discount. If you don't hear back from them, you can also get in touch with the team from SheerID here, so that they can check your status again.