You can delete mappings for key mapping entities only.

What causes this issue?

You are attempting to delete mappings for value mapping functions or
codes, such as company code, business area or country code.

System Response

This is <ZH>not</> supported with the <LS>Central Finance</> mapping
tool and the mappings for value mapping entities are <ZH>not</> deleted
from the <LS>Central Finance</> system.

How to fix this error?

Select only key mapping entities, such as customer ID or G/L account for
deleting mappings from a CSV file.
You can still display or download mappings for value mapping entities.

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.