SAP Message WTADDI412 - Material & is not an additional

Diagnosis
You are entering additionals for amaterial. You can only choose a material for use as anadditional if its material type has beenflagged for such use.
The material you have entered (&V1&) does not have this flag.

Procedure
Find the additional by means of the matchcode for the material type,making sure that you enter a material type that is defined for use asan additional.