Overview:
This error typically occurs when your QuickBooks Desktop application is configured to disallow negative quantity adjustments.
Troubleshooting
Log in to QuickBooks as an admin and ensure that you are in single-user mode.
Click Edit > Preferences > Item and Inventory > Company Preferences > Warn if not enough inventory to sell > disable the option “Don’t Allow Negative quantities” and select other available options as per your requirement > OK.
Once done then try to post the order again from Webgility Software.
Feel free to reach out to Support by initiating a chat if the issue persists.