In the case of Fixed Fee projects, the uninvoiced amount is calculated by taking your total project fee amount and subtracting the total amount due from each linked invoice (more specifically, the total amount due for each line item on the invoice that was linked back to the project).

When the uninvoiced amount is red and has a negative sign, it means you've billed more than your set fee amount for the project.

If you'd like to see your uninvoiced amount as zero or a positive amount, you can edit your project fee amount.