When you want to add another user to your plan, you should do it from Account Management at SelBuk.com > Login > Account management > Plan & Services > Active users

Login

Account manegement 

User Id / Password > Login

Plan & Services

Active User > Select > Update

Click on Users & Devices 

User > Column Edit > E to edit the information require on the email-user

My Account > Complete all require fields * > Update

Each new user should have their own email/password

Remark: once the new user is created, you should install the SelBuk version available at the Apple AppStore and enter with the registered username and password. The system will ask you to download from the cloud service.

Keep in mind: each email-user should be only registered either on an iPad or iPhone.