Looking for a specific variable

Is there a specific variable for the full amount a client owes across all of their invoices?

I thought it’d be $balance, but that’s only the balance for the invoice in question. I’d love a “YOU OWE US THIS MUCH MONEY IN TOTAL” variable, if possible.

In the invoice PDF I believe you can use $client.balance.

That doesn’t work in Notifications, which is where I’d like it to be.

Will add it in the Invoice for now, though.