Subtract Invoice amount from Total based on Status, in Parent-Child relationship

Hi all,

I am new to create sheets, but I am trying to create a solution to track forecasted invoices that need to be sent out. I want to put each invoice total separately and when the status is marked as "Complete" I would like to have it subtracted from the Contract Amount to show the Contract Balance. I set it up so the invoice amounts are subtracted from the Contract Amount, but it does it when I input any amount, which is not helpful. I currently have

=[Contract Amount]@row - SUM(CHILDREN([Invoice Amount]@row))

in the "Contract Balance Column" but can't figure out how to make it a SUMIF the Status is "Complete" with the parent child relationship.

Thank you!

Majesta