I developed an app with a simple implementation of google in-app purchases: the App is free and can be upgraded to a premium version via In App Billing (managed product) providing some additonal features.
Now I want to provide a special deal selling my in app product for half price for some days (maybe using a general promition code, but that's not important).
I did a lot of research and found a solution how to create a promotion for in-app purchases (for free) using promo codes, or how to set an app on sale (only available for chargeble apps).
Isn't there any posibility providing a special offer for my product?
Thanks a lot for your answer!
Raspberry
Register another in-app product with a reduced price, make it available in the app on some days only. This will be quite open to user fraud, though - change the current date on the device, and enjoy the discount any day. That's barring more sophisticated kinds of fraud, like attaching with a debugger and adjusting the return value of Calendar.getTime().
If it was possible to change the price on an IAP product from the app, there would be another massive avenue for attacks.
In general, when it comes to Android billing, you can't trust the device.
One safe way to do that would be to run a back-end with a connection to Google Play (either HTML scraping or API) that would modify the price on a schedule. I had some good results running Google Play console in headless Chrome driven by Puppeteer (and before that, in PhantomJS).