Idea

it sounds like, rather than a normal currency or energy model, you have one where the rate of currency generation is tied to the specific inventory items in the player account. This isn't far-fetched, but it is very game specific, and it's something you'll want to tune the values on post-launch, as you see how it's used. So here's what I'd do: Create your currencies and items, and then make some Cloud Scripts which the player calls periodically to sync with the service on the last sync time and the amount of currency earned based upon a) the items in the player's inventory and b) the regeneration values for those items, which you'll store in Title Data. You won't even need to call this very often - just call it on player sign-in, to get an initial sync of the info, then again when the player does something that requires the currency values to be authoritative, like spending any currency. That way, you can block any cheating, since all the important calculations will be on the server side.

Ok, if my server or my cloud script is managing currencies, is there transaction support with rollback possible?

My update currency model would batch all the changes into a block and send the block to update all the currency if the currency needs to get bumped. . .

or should i keep a last sync value per currency . . .

or is this not necessary?

Yes, if you're using the Server/AddUserVirtualCurrency in Cloud Script (or your own custom server), you'll be adding the currency to the player account, and it can then be used via PurchaseItem to buy things from your catalog. For rollback, you have the option of revoking items and re-adding the currency (either/or) via API calls or the Game Manager.

The way to manage the currencies would be:

• On sign in, calculate the current amount for the player, based upon the last value and timestamp you recorded in User Read Only Data (so that the user can't cheat it from a hacked client).
• Show the player a continually updated balance locally, since you're constantly recalculating. Don't write this to the account online, as it's not needed.
• When the player takes an action that should have an authoritative check, like making a new building, use Cloud Script to ensure you have a server-authoritative way to do this (again, to prevent cheating).