Problem
Payment recorded with incorrect amount and applied to wrong invoices after export to QuickBooks.
Solution
You can fix incorrect payments by opening the accounting period and editing the payment amount. Then manually re-apply the payment in QuickBooks.
Fix incorrect payment already exported to QuickBooks
Delete the incorrect payment record from QuickBooks first.
In ServiceTitan, go to the Accounting tab.
Find the accounting period for the payment you need to fix.
Click Action > Open Period on the right side of that period to open that period.

Go to the invoice record that has the incorrect payment applied.
Unapply the payment from the invoice.
Go to the customer's profile.
Find the payment record you need to fix.
Click on the payment record.
In the amount field, enter the correct payment amount.
Save the changes.
Manually re-apply the corrected payment in QuickBooks.