Entry for flow type &1 with +/- sign &2 already exists

What causes this issue?

The entry already exists for flow type &V1& with plus/minus sign &V2&,
which is to be entered during the conversion.

System Response

The system does not carry out the conversion for this entry. The
existing entry remains.

How to fix this error?

Check your Customizing settings to see whether the existing entry is
appropriate for this flow type. Delete any incorrect entries and then
carry out the conversion again.

Error message extract from SAP system. Copyright SAP SE.