3582230 - Error happens when assigning apportionment structure: Allocation U is not allowed for this apportionment structure

When changing the apportionment structure in material master, below error happens:

Allocation U is not allowed for this apportionment structure

Message ID: A4006

SAP S/4HANA Cloud Public Edition

The assigned materials in the apportionment structure are all set as co-product. It's not supported.

Adjust the materials, and make sure at least the main material is not co-product.

A4 006, source structure, apportionment structure, allocation , KBA , CO-PC-OBJ-2CL , Cost Object Controlling (Public Cloud) , Problem