Forecast period exceeds financial plan validity; extend plan validity

What causes this issue?

You are trying to forecast beyond financial plan validity.

System Response

As forecasting for all plan periods has already been completed, system
throws this error message.

How to fix this error?

If you want to continue forecast for periods beyond financial plan
validity, adjust the financial plan validity accordingly and then
continue.

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.