No quantity has been entered for the primary output

What causes this issue?

You have not entered a quantity for the primary output in the I/O
Materials and I/O Substances cost views. This value is automatically
replaced by the base quantity or the reference quantity entered in the
cost view. Since the relationship between the base quantity and the
primary output quantity is determined first in costing, the lack of one
of the two quantities means a simplified calculation must take place.

System Response

The relationship between the base quantity and the primary output
quantity is not determined in the calculation.

How to fix this error?

If you want the relationship between the base quantity and primary
output quantity to be determined, specify a value for the primary
output.

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.