So the licence management code is integrated into PCDB SuDoku Solver, and appears to be working to the extent that I can test it without first publishing the app. However, it's thrown up some issues with my use of threading (and you can't write a serious Android app that doesn't use multi-threading) so I need to do a thorough overhaul of that. The issue is that I had assumed there is only one background thread, the one that solves puzzles. But there may be others, such as the licence handler callback, which need to fit into the same architecture. It should be sorted by checking specifically whether or not you're on the UI thread, rather than in a specific background thread. But there are bound to be other consequences. Need some detailed testing once this is sorted.