Maintain operand values for operand &1

What causes this issue?

You have not defined any operand values for operand &v1&, however,
operand values are required for this operand in order to calculate the
rate.

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?

Define operand values for operand &v1& or specify the operand values
for the operand in the rate category facts or installation facts.
Please note the function of <DS:DE.ERSATZWERT>replacement values</>.

Error message extract from SAP system. Copyright SAP SE.