Invalid value for request flag. Valid: empty, 1, 2

What causes this issue?

You entered a value that is not allowed for interface parameter
REQUESTFLAG.

System Response

The system cannot select any allocation tables.

How to fix this error?

Make a new selection and leave the interface parameter REQUESTFLAG
empty or set one of the following values:

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

1: Selects allocation tables for which requested quantities have still
to be entered by the date specified.
2:Selects allocation tables for which requested quantities have still
to be entered or can still be changed by the date specified.

Error message extract from SAP system. Copyright SAP SE.