what is the best way for in app, including virtual currency, syncing over cross platform

hi, as the title says i want to have the in app purchases of game coins, and i will have the gaem over cross platform so it needs to be synced, so basically it needs to be saved over the server. i have used soomla before, heard a lot about prime31, now i have noticed the unity provides its own service of in apps, which is essential for cross platform, i would really like to implement unity ones, but i don't see anything like virtual currency in that. i am open to suggestions, i want something easy and quick to implement.

Also if we forget about the server and cross platform syncing, then how do we make playerprefs secured to not be easily tampered, any suggestion