You are trying to add an extension field to a data source or a report for a specific business context, via the further usage link, but the list of data sources or a report is empty.
In this example, the business context is Items to be Invoiced - General Information.
Reproducing the Issue
1. Go to Customer Invoicing work center.
2. From the Common Tasks view chose the New Manual Invoice sub-view.
3. On the New Manual Invoice page select Adapt then Enter Adaptation Mode.
4. A Confirmation pop-up box opens, press on Yes button.
5. In the Adaptation Mode page, click on Adapt then Edit Screen.
6. On your right-hand side, in the Adaptation Panel, under Extension Fields, select any field.
7. Click on add and enter the Field Type and the Label name then save.
8. Highlight the chosen field and Click on the Further Usage link.
9. In the Further Usage of Extension Field page, go to the tab Data Sources and Reports.
10. You will see that the list is empty. e.g. no Data Sources and Reports are shown.
The screen New Manual Invoice doesn't display an Invoice Document but rather an Invoice Request Document.
If you enter the adaptation mode for a document from view Invoices and Credit Memos you can extend the invoicing reports with new fields as in this view Invoice documents are contained.
KBA , SRD-MD-PRD-PRD , Product , How To