@INAAYAT DHAR , thank you for reaching out to us. Happy to help. Did you, by any chance, sign up with the same email ID to any other Azure subscription?
If yes, this happens.
If not, then there can be any of the two reasons: Your educational institute is not recognized/partnered or eligible with/for Microsoft. You can refer to the FAQ page OR your school admin might have not granted access to you to register for Azure for Students. Check out similar issue here, where the user had the latter reason in their case.
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