Enter at least one quantity string

What causes this issue?

You have not entered a <GL:quantity_string>quantity string</>.

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?

Enter a quantity string or an interval.
Do you want to <DS:TRAN.OMBQ>check</> (in the table of movement types,
view "Update control") which quantity string is used for a movement
type?

Error message extract from SAP system. Copyright SAP SE.