Please carry out forecast for material & in plant &

What causes this issue?

You wanted to plan a material for which there are no forecast values.

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?

Either maintain the forecasting view of the material master record
whereby you must manually enter consumption values and then carry out
the forecast calculation.
Alternatively, you can maintain the forecasting view of the material
master record whereby you manually enter the forecast values and then
carry out material requirements planning again.

Error message extract from SAP system. Copyright SAP SE.