android - Detect if free app has been purchased for money -

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we planning on changing our paid app, "free" (demo) app in-app purchase unlock full game.

our problem making transition have customers who've paid app. therefore need ensure wont have pay they've bought once. have looked every possible solution can think of, without luck.

licensing out of question, return valid free apps.

any suggestions appreciated. fallback we'll have create 2 apps, rather prefer keep single one.

regards jannek

edit:

thanks feedback. didn't find solution, ended using first achievement unlock game default. covers 80% of our players. unfortunately 80% of pirates. remaining 20% setup token server, can unlock game entering last 8 digits purchase info.

this allows give out promo codes on google play.

a couple of unsatisfying solutions:

  1. update app before make free. collect ids somehow of people use , record them. downside miss people update or use app.

  2. release paid app new package. convert old 1 "pre-paid licence". can detect whether licence app installed or not new one. downside lose ratings , reviews.


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