Chromecast devices may be compatible depending on OS version
Installation via 'Send files to TV' app
Note: Your phone and set-top box must be connected to the same Wi-Fi.
First download the Flix1 TV app on your phone.
Install the 'Send files to TV' app on your phone from Google Play/App Store and launch it.
Open Google Play on the set-top box and install the 'Send files to TV' app then launch it.
Select 'Receive' on the set-top box app.
On the phone app select 'Send' and choose the downloaded APK file. (On Android go to the Download folder and sort by date descending to find it easily.)
A screen to select the target device will appear.
Select the set-top box to begin the file transfer.
Once transfer is complete press 'OK' on the remote and select Open to install the app.
Installation via USB drive
Download the Flix1 TV app on your PC and copy it to a USB drive.
Connect the USB drive to the set-top box and open a file manager app. (CX File Explorer or any other file manager will work.)
Select the APK file from the USB drive and install the app.