Currency could not be converted from &1 to &2

What causes this issue?

Your attempt to convert &V1& to &V2& has been unsuccessful. This can be
due to different reasons (see error code):
no exchange rate has been specified,
the result is too high,
no factor was found,
"NO_SPREAD_FOUND" error,
other error.
The current <ZH>error code</> is &V3&.

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?

Your actions depend on the error code:
RESET N1
Maintain an exchange rate in the customizing system by performing the
following steps:
In the customizing system, follow the menu path Global settings ->
Currencies.
Choose "Enter exchange rates".
Check the relevant amounts, working hours per period etc.
In the customizing system select the menu path Global settings ->
Currencies.
Choose "Define factors for currency conversion" and add the conversion
factors for rate type 'M' from &V1& to &V2& and from &V1& to &V2&.
The cause is presumably a program error; contact SAP.
The cause is presumably a program error; contact SAP.

Error message extract from SAP system. Copyright SAP SE.