Open Messenger from your app drawer. Log in as usual. If you have two-factor authentication enabled, you will receive a code via SMS. Test a text message and a short voice call to ensure codecs work.

Enable Unknown Sources: Go to Settings > Security and toggle on "Unknown Sources." This allows your phone to install apps from third-party files.

APK stands for . It is the raw file format Android uses to distribute and install apps. By downloading a specific APK for Android 4.4.4, you bypass the Play Store’s compatibility check and manually install a version of Messenger built for your OS.

If you want, I can: