You will come across this error if you want to post the billing document for the Sales order line item with item categoy TAS for 3rd party sales scenario besides other cases. In standard case, system allows posting billing document only after the vendor is paid. That is steps to be followed are: VA01 – ME21N (creation of PO with reference to PR in Sales order) – MIGO – MIRO – VF01. If MIRO step needs to be avoided, please change the following settings:
1. VOV7 for the item category: Change the Billing Relevance to B.
2. VTFA for the Item category (Target Billing document and Source Sales Doc type) change the Billing Quantity Indicator to E.