Comentario oficial
We do this to keep people from creating multiple abusive accounts to get multiple free trials. This message only occurs when the account's purchased point balance is zero.
They students are free to continue to use the system but they won't get the 15 day free trial of the Pro level. There is still plenty that can be learned using the Free tier.
As the message says: "please either subscribe or pay for processing points". As the educator you could provide your students with the materials you need to take the course. If you give a non-zero amount of points to your students they would be able to use their trial. We have made your account a point distributor so you can do this.