Why the Sync Error occurs
This error occurs when a bill cannot sync to Oracle NetSuite because the account field is blank in Bill.com, but is required on a custom form in Oracle NetSuite.
How to Fix the Sync Error
Add an account to the bill in Bill.com, or if the account field is selected as mandatory on a custom form, switch to the standard form as the preferred form or to create a brand new custom form without selecting a non-default field as mandatory. Once a field has been checked as mandatory on a form, the sync will continue to call for it even if it's unchecked.