Cost distribution will be quantity-based

What causes this issue?

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

System Response

No valid apportionment structure for the material was found in the
plant. Costs are distributed to the joint products based on the output
quantities in the valuation unit.

How to fix this error?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.