Educational discount request not approved

Hello, I’ve submitted an educational discount request, attaching the first page of the employment contract of my school. It contains all the anagraphics of me and of the school where I work. Nonetheless, I received an email containing the text: “The item you uploaded is insufficient to demonstrate your current academic status. Please try again.”
Unfortunately I can’t reply to the email I received, so I’m posting a new message here. Could you tell me what’s missing in the attachment?

I have all the requisites to apply:

To apply for an educator or researcher discount, you must:

Be an educator, faculty member, or researcher
Have a verifiable school-issued email address or upload documents that prove your school affiliation
Have a GitHub user account

Thank you

© 2017 GitHub, Inc.
with by
GitHub Education