Subsidy (preference) amount not set

What causes this issue?

Due to the subsidy indicator, the system expects the user to enter a
value in the field for the subsidy (preference) amount, so that the
amount of subsidy can be calculated.

System Response

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

How to fix this error?

Enter the subsidy (preference) amount, if required.

Error message extract from SAP system. Copyright SAP SE.