This feature is only available in alpha. We will publish more information next week.
In a nutshell, you need to map 3 fields in PAM:
The Grouping field will be the name of the group (the limit will be applied to multiple items as a group),
The Limiting field will establish how many items from can be purchased from the group.
The Reset Limit is optional and establishes the month when the limits are reset. If it is left blank then the limits will be reset at the beginning of the next year.
You give the same group name to all the items that you want to associate together (and of course the same limit and month date).