ISO code & is not assigned to a currency key in the valid time period

What causes this issue?

No internal code assignment was found for ISO code &v1& for currencies
(table TCURC). Either the internal code does not exist, or it is not
assigned to the ISO code.

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?

Assign an internal code to the ISO code.

Error message extract from SAP system. Copyright SAP SE.