SAP Message WXP610 - Only one quantity key figure can be assigned to interface &1

Diagnosis
You want to create promotions
using interface &V1& forplanning step &V3&. To do this, you must assign aquantity key figure (promotional quantity) to the interface. Allplanning key figures with units of measure thatare assigned to planning step &V3& can be used for creating yourpromotion.

System Response
No promotion can currently be created using interface &V1&.

Procedure
Assign a quantity key figure to interface &V1&.