Path: Settings > Security/Privacy > Install Unknown Apps > Enable Browser.
If the file fails, download it again to ensure it was not damaged during the download process. Display Tester for Android - Download the APK from Uptodown Download Display Pro apk
Stick to reputable repositories like APKMirror, which check for file integrity and signature matches. Path: Settings > Security/Privacy > Install Unknown Apps
This often occurs if a free version is already installed. Uninstall the free version before installing the Pro APK. Download Display Pro apk