Selection ignored without entry for indicator <ENTER>

What causes this issue?

If the 'settlement' indicator is not active, processing ignores the
associated selection input.

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?

If necessary, set the indicator.
Continue with <ENTER>.

Error message extract from SAP system. Copyright SAP SE.