Kindle fire 7 won't install app

I built the Mobile Functions app and created the .apk.
The app installed and worked on my Android 12 phone.
However. my Kindle Fire 7 Android 5.7 OS won’t even try to install it.
Is this because it’s too old of an OS?
How can I make an AppStudio app that will run on older Android devices?

To control this, build using an older Android engine. You can do so by adding this line to your config.xml property:

<engine name="android" spec="11.0.0" />

OK, thanks.