If you have a QTS 4.3 and previous Xopero installation on your QNAP, remove it before proceeding with the following steps - you will keep your data.
After Container installation follow these steps:
To install the package, go to My Apps and select Install Manually option.
Then in a window, you have to select the location of the package and click Install.
After performing the above steps, the installation will start. During the installation, in QNAP logs will display the information and warnings about the installation process. The screenshot below shows the correct database migration process.