Rule &1: A time period and a calendar have been entered. Check entries

What causes this issue?

A time period and a calendar have been entered in this rule. This
prevents the system from generating settlement periods correctly when
creating the next billing/invoice date.

How to fix this error?

If you require a different billing/invoice date, use the rule for
determining a different billing/invoice date. In this rule, you can use
the calendar and/or the time period to change the original
billing/invoice date.
If a time period has been entered in the rule, the system adds or
subtracts the period to or from the original billing/invoice date. When
you then look in the calendar, the system will always search forwards
from this new date.
If you do not enter a calendar or a time period, the system searches
for the next selected date from the original billing/invoice date.

Error message extract from SAP system. Copyright SAP SE.