14 September 2017
We have made some fixes, try again to upgrade your backup plan and please confirm if everything is ok.
As for inviting users to the account, please refer to: https://skyvia.com/resources/docs/index.html?account_users.htm ("Inviting and Deleting Users from Account" section).
To invite users, open your Account page, enter the email of the user you invite to the Enter user email to invite box and click the + button. Please note, the invitation emails are not sent in this case. When the invited user logs in to his Skyvia account (or signs up, if the users is not yet registered), he can choose whether to use his default account or the account of the user that invited him.