& & cannot be converted to &

What causes this issue?

You want to convert the amount of &V1& &V2& into &V3&. However, no
average rate was defined for converting &V4&.

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?

Maintain the exchange rate with exchange rate type "M" from &V3& to
&V2& for &V4&.

Error message extract from SAP system. Copyright SAP SE.