Exch.rate categories &1 and &2 are not defined consistently

What causes this issue?

The definition of these exchange rate categories in Customizing is not
consistent with the reference currency and the corresponding middle rate
(where applicable).

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?

Enter the same reference currency (or blank) and the same middle rate
(or blank) for the corresponding exchange rate categories.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.