Hi
First of all Microsoft Certication related Q&A are answered in different forum.
https://trainingsupport.microsoft.com/en-us
How to get verified :
Assuming you have a personal Microsoft outlook.com ID ( if not create one).
Login with personal ID & Try to register any exam with peason VUE , update your personal details and in discount section put your student ID and link the student ID with Personal ID . You will recieve an OTP on student mail ID ( sometime OTP take longer to come on mail ) and once you student is succesfully linked to personal ID . If your student ID really has a discount , you will see it automatically . and proceed to register your exam for free.
Second option : You mention you need AZ-900 certification for free , this can also be achieved by attending MS training event . Once you attend this training using your personal ID and then tried to book exam with ID you will get free certification coupon for that exam.
Schedule of event for AZ-900 : https://events.microsoft.com/en-us/allevents/?language=English&clientTimeZone=1&search=Microsoft%20Azure%20Virtual%20Training%20Day:%20Fundamentals
Register here for 25th May 2023 Event : https://mktoevents.com/Microsoft+Event/395762/157-GQE-382?wt.mc_id=eventscatalog
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