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Hello Adrián
You are probably entering a Personal Email (like Gmail, Hotmail, or Yahoo) in the box.
The Rule: The system only accepts emails given to you by your school (usually ending in .edu, .ac.uk, or your university's name). Check the email: Make sure you are typing your school email address, not your personal one.
Type it manually: Do not copy and paste it. sometimes "autofill" adds a hidden space at the end which causes this error.
Try a different browser: If Chrome Incognito didn't work, try using Microsoft Edge in InPrivate mode.
If it still rejects your school email:
Your school might not be in Microsoft's "automatic" system yet. You will need to contact Microsoft Support directly so they can look at your Student ID card and approve you manually.
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