Define Account Assignment Group

Field found in Material Master Sales Organization 2.
To define the General Leger posting :-
IMG -> Sales and Distribution -> Account Assignment/Costing -> Revenue Account Determination -> Assign G/L Accounts

With this link, the material that used this account assignment group will be posted with the desired G/L accounts during Billing.
User will not be able to Release the billing document to Accounting if this is not setup.
If you happend to assign it via Cust.Grp/MaterialGrp/AcctKey, then you can let your user use this report to check the material assignment.
* Transaction code VKOA