QuickBooks Online rejected a settlement because the payment came out less than the charges. This usually happens when QuickBooks applies a credit to the payment by itself.
How to fix it
In your QuickBooks Online settings, turn off "Auto Apply Credits".
In ConnectBooks, go to Accounting Export. Click the 3 dots on the settlement and choose "Delete from QuickBooks". If you see Settlement, COGS and Both, pick the one that shows the error.
When the status shows "Deleted", click the 3 dots again and choose "Resend to QuickBooks". Pick the same option as in step 2.
Frequently asked questions
I did this and it still fails.
Contact support and we'll look at it.