Forecast only possible if you enter a period indicator

What causes this issue?

You wanted to do one of the following:
Enter <DS:GLOS.forecast_value>forecast values</> manually as a basis
for the <DS:GLOS.planning_run>planning run</>
Execute a <DS:GLOS.forecast>forecast</>
Since the system manages forecast values and consumption values on a
period basis, you must specify the periods to be used
(for example, day, week, month, or period according to the fiscal
year variant).

How to fix this error?

Enter the period indicator required.

Error message extract from SAP system. Copyright SAP SE.