Field &1 is not used for the selection (module &2)

What causes this issue?

In your program you are using function module &v2& to select CO
transaction data. Field &v1& is the selection criterion. This field,
however, is not a key field for the table to be read and is therefore
ignored by the system for the selection.

System Response

The database selection is executed without the characteristic value for
field &v1&. This means that the number of hits could differ
considerably from the result you intended.

How to fix this error?

This warning is only issued in SAP Systems and requests that you check
the table of selection criteria. The consideration of field &v1& must
be executed from the application itself.

Error message extract from SAP system. Copyright SAP SE.