I believe you should turn on the setting, allow install from unknown apps for the browser of your mobile. See here
plantdoc2018DBasakBetaKoder
asimjib93
@eyepictures8
Another Reasons that may cause Problem to install app:
- Play Protect is on: That does not allow you to install any package for unknown source.
Solution: Turn it off during installation, you can turn in on again after installation. - Install Apps from unknown source is off: It will also not allow you to install Apps from unknown source. In this case you have to turn on the setting for the browser of your mobile by which the apk was being downloaded.
Example: Say you are scanning the QR code (after Building apk) to Kodular companion)/other QR code scanner to download the apk. Now notice this thing leads you to a browser where downloading turns completed. Go to settings and make sure that Install unknown apps setting is turned on. That’s it.