how to call a static method in another static method in the same model laravel

I created a static method to help me know what mobile OS app my users upload.

public static function knowAppPlatform($file){
    $extension=  $file->getClientOriginalExtension();
    if ($extension=== "apk"){

        return 'android';
    }
    elseif ($extension=== "appx"){

        return 'windows';
    }
    elseif ($extension=== "ipa"){

        return 'ios';
    }
}

Then i tried to call that same static method in another method in the same model. but it keeps returning a null, it works fine outside the model but not inside.

 public static function uploadScreenshot($file){
    $platform = static::knowAppPlatform($file);
     dd($platform);
    $name = Auth::id() . 'screenshots' . time(). '.' . $file->getClientOriginalExtension();
    $name = $file->storeAs('mobileApps/screenshots', $name);
    return $name;
}

I have researched here on stack overflow and implemented some of the answers, yet no show.

I have tried,

$platform = static::knowAppPlatform($file);
$platform = self::knowAppPlatform($file);
$platform = \App\model\students\App::knowAppPlatform($file);

via Chebli Mohamed