Generally, the developers that works with Hybrid apps like Cordova, Ionic, Phonegap etc. tend to Download the entire Android Studio as an insurance policy. We think that everything should simply work once the SDK is installed and that's it, however with the latest release of Android Studio 2.3, many developers have faced the "Could not find gradle wrapper within Android SDK" (although this error goes back to older versions).
Solution
Extreme problems require extreme measures, although many solutions that you may find in Internet tell you that you should update the environment variable ANDROID_HOME path to the current path of the SDK, that solution is most likely not to work as if you have installed the latest version of Android Studio, that should be done automatically.
The real solution however is very simple, as first step download only the Command Line Tools from the Android SDK website:
The SDK tools package is only a .zip file, the size file of the ZIP tools in Windows for example, it's about 300MB. Once the download finishes, extract all the content of the zip inside the tools folder of the current SDK in your pc e.g in Windows C:\Users\<username>\AppData\Local\Android\sdk\tools: Then the problem should be solved and you will finally be able to build your APK:
Happy coding !
