The implicit foreign exchange rate was set to 1

What causes this issue?

You wish to carry out a manual valuation for the position on &V1&. To
enable this, book values must have been defined in the system as at
&V1&.
The system determines an implicit foreign exchange rate from the book
values in position and valuation currency. This is not possible in this
case since at least one of the two book values is 0.

System Response

The implicit foreign exchange rate was set to 1.

How to fix this error?

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

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.