Backlog by Location

Ok so I'm still unable to figure out the DAX to create a measure for backlog by date and store.

I've gone through a bunch of the suggestions and it seems cumulative totals are pretty common, but not backlog, and even then, most are for a single item (like counting backlog of tickets).

I've updated my model so I have 2 fact and 2 dim tables.

Fact tables are for capacity by store and day and pallets build by store and day.

Dim tables are my stores table and my financial dates table

I'm really not understanding for some reason, how to create the cumulative backlog by day and store....

My overall requirement is:

If the store is in an over capacity situation (ie they have more pallets than capacity), then we must calculate the cumulative backlog until they dig themselves out of the hole.

If the store is under capacity, the totals reset (ie you don't gain extra capacity... so if you have a capacity of 5/day and yesterday you only got 3 pallets, you don't suddenly have capacity for 7 pallets today).

It's a pretty complex requirement, and my experience with DAX is still at a very biginner level unfortunately.

I'd appreciate any help walking through a solution so that I can understand what's being done and why....