OBSOLETE:
In order for the application to work properly, you need to Restore bookify.bak to your SSMS.
To do that, copy bookify.bak to the Backup folder from your installation path (usually C:\Program Files\Microsoft SQL Server\MSSQL16.SQLEXPRESS\MSSQL\Backup).
From SSMS right click on Databases -> Restore Database...
From Source select Device, then click on the 3 dots to browse. In the open window, select File from Backup media type, then click on the Add button.
Browse for the Backup folder mentioned before, click on bookify.bak and then click OK. Hit OK again and again on Restore Database window.
After this process, you can run the app successfully.
UPDATED: Moved the database from SQL Server to Oracle. Everything should work just like before.