Mod apk is a modified version of the original application which can be downloaded from the Google Play Store. A modified app has all of the features and benefits of the original application for free, without any cost. Besides being free of charge, it is often accompanied by various in-app purchases. However, it is important to note that installing a mod apk is not safe. It has no security check and is not recommended for users.

Basically, it is an APK which has been changed by third parties to add extra functionality. Some of these apps require specific permissions, which can result in invalid license error. In order to fix this, you need to download a trusted mod apk and install it. Once you have the modified version, you can use it safely. This will avoid any risk of the original APK. While it sounds like an advantage, it can also be dangerous if the permissions are changed.