Based on the datastore warning that was provided, it seems like the datastore API isn’t enabled for your game, which is easily togglable in the game settings.
This is what I found for your error (403)
Source: Data Stores
Here’s how to enable the service in the game settings:
Source: Data Stores
If the error persists, try it in the real game rather than studio, since data typically doesn’t save in studio correctly unless you use a game:BindToClose() function, add a wait and save data from there. If the error persists even further, you can respond to this message and I can take a look at your code, but for now make sure these steps are done before anything 