I did this same step last night (still very much going through the guide too, too much stuff going on!) and I had issues in linux so had to book into Windows but worked fine then. Did you install the java SE that is specified? I downloaded the zip, extracted, installed java SE from the github recommendation and the APK generated fine (which then installed fine).What's what i am trying to do, the .bat file to build it doesn't when following RGC's video guide.