Hello,
I am working on my new game & I would like to offer one feature for free for limited time, for example 3 days free or 10 free plays, etc… Could you tell me what is the most secure way to implement some trial mode similar to those into the game 
Thanks!
If this is for Android you’ll probably be OK, but I’m pretty sure Apple won’t allow this. i.e. They’ll reject the app.
As far as implementation, simply track the date and time the app is first run in a file (saved in the documents folder). Then, when the current day is past your trial period disable your features.
That is the general approach. Specifics will depend upon your app/game.
Note: You also asked about making this secure. I wouldn’t bother. No matter what you do, the effort to make it secure will not be worth it. Those who want to cheat the system will do it.
One more note. You’d be better served thinking in terms of consumable IAP features. i.e. Tokens or some other virtual currency. This is an acceptable approach by Google Play and Apple.
Then you can start a fresh install with M tokens and let users buy more.
-Ed
Thank you Ed on your answer! I was thinking about the same thing to save a record in a file, but the problem is that when user uninstalls the game, so is the file deleted. After re-installing it, he/she will get it free again.
If this is for Android you’ll probably be OK, but I’m pretty sure Apple won’t allow this. i.e. They’ll reject the app.
As far as implementation, simply track the date and time the app is first run in a file (saved in the documents folder). Then, when the current day is past your trial period disable your features.
That is the general approach. Specifics will depend upon your app/game.
Note: You also asked about making this secure. I wouldn’t bother. No matter what you do, the effort to make it secure will not be worth it. Those who want to cheat the system will do it.
One more note. You’d be better served thinking in terms of consumable IAP features. i.e. Tokens or some other virtual currency. This is an acceptable approach by Google Play and Apple.
Then you can start a fresh install with M tokens and let users buy more.
-Ed
Thank you Ed on your answer! I was thinking about the same thing to save a record in a file, but the problem is that when user uninstalls the game, so is the file deleted. After re-installing it, he/she will get it free again.