Forecast includes only historical values as from & --> F1

What causes this issue?

You want to carry out the forecast for the historical values from &v2&
to &v3&. However, historical values prior to &v1& are zero. The system
response to this situation depends on the user. The following responses
are possible:
1. The entire historical period is included nonetheless.
2. Historical values before &v1& are not included.
The user setting that has been made for you corresponds to variant
&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?

You can change the historical values in the period from &v2& to &v3&
manually, regardless of the user setting. If variant 2 applies and zero
values before &v1& are then corrected, the historical period used by
the forecast is extended to include this date or period.

Error message extract from SAP system. Copyright SAP SE.