If Instander APK is not installing, several factors could be at play. First, ensure that you have enabled the option to install apps from unknown sources in your device's security settings. Second, check if the APK file you downloaded is complete and not corrupted; downloading from a reputable source can help avoid this issue. Additionally, ensure your device has enough storage space and is running a compatible version of Android. Lastly, there might be conflicts with the existing Instagram app, so try uninstalling the official app before installing Instander APK. If problems persist, restarting your device and attempting the installation again can sometimes resolve the issue.