I just registered as a free trail of wikitude four days ago, and I'm following the tutorial here: SETUP GUIDE CORDOVA CLI. I copied and pasted the key they sent me to the WikitudePlugin.js as they did in the tutorial. But when I build and run my project, it just gave we a watermark of "License key is missing". I was really confused.
If you run cordova build to build the android project, your WikitudePlugin.js will not be built into the project for some reason. So how I solved this problem is to copy and paste the key in ~/<Project Name>/platforms/android/platform_www/plugins/com.wikitude.phonegap.WikitudePlugin/WikitudePlugin.js again after I build my android project.