New base date is earlier than old base date &

What causes this issue?

You have changed the base date of the reservation, and the new base
date is earlier than the old base date.

System Response

The system allows the entry: the warning is intended to prevent your
entering a wrong base date.
The new base date is used to change the <GL:date_required>"date
required</> in all reservation items.

How to fix this error?

INCLUDE NA_EINGABE_PRUEFEN

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

Error message extract from SAP system. Copyright SAP SE.