Hey Роман Омельченко
The error is due to an unmanaged AAD tenant issue and offer the following steps to sign up:
Open an InPrivate session of Internet Explorer and go to
(https://imagine.microsoft.com/azure). Log in using your Microsoft Personal Account (if you don't have one, create it from [http://signup.live.com]). Complete the verification process using your Microsoft School Account address or activation code. Continue the activation of the Azure plan using the Microsoft Personal Account.
Also there is a possibility 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.
Please "Accept as Answer" if it helped so it can help others in community looking for help on similar topics. thanks much.