A short summary if I may:
- Predictive Text Input (PTI) requires the valid Sailfish licence on your Jolla account to make the app appear in Jolla Store
- PTI must be installed from Jolla Store (downloaded and installed like any app)
- The phone must be restarted to complete the installation of PTI (as a deviation from most other apps).
After this, the bar of predicted words appears on top of the virtual keyboard on various apps.