Financial documents: exchange rate from & to & on date & not calculated!

What causes this issue?

After you entered the number of the financial document or the
depreciation percentage rate, the system tried to calculate the
exchange rate between the financial document &V1& and the local
currency &V2& at &V3&.
The system could not calculate the <GL:exchange_rate>exchange rate</>.
INCLUDE 'NA_NO_PROCESSING_2' OBJECT DOKU ID TX LANGUAGE EN

System Response

The system does not allow the entry.

How to fix this error?

Check if a valid exchange rate exists for this currency on &V3&.
If not, define the relevant exchange rate in Customizing, if you are
authorized to do so.
<DS:TRAN.OB08>Define exchange rates</>

Error message extract from SAP system. Copyright SAP SE.