Welcome to the Community, Mconnolly19! 

Currently, QuickBooks Online doesn't have a change order feature, and transactions can't have negative balances. To comply with the system's requirements, you'll need to ensure transaction amounts are 0 or greater.

However, on an Estimate, you will be able to add a negative amount only if there's a higher amount along with the negative order. Here's a screenshot for your visual reference. 

If you need further guidance, please don't hesitate to Reply to this thread.