There is a 3-day delay for orders from WM Backend to sync into QBO online. This allows orders to be canceled, modified, etc, and then syncing the final invoice only. If it has been more than 3 days and the invoice isn't synced please report to developers by adding a task on the Monday development board and assign to Bharat.
https://demo.wmprinting.com/admin/quickbook_sync_setting.php?id=36