Flag 'TODAY' set, as calculated value date already overdue

What causes this issue?

The 'TODAY' indicator (<LS>intended for immediate payments</>) is first
set on the basis of the best-priced payment method. The final decision
of when this payment is carried out can only be made at a later date.

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?

Error message extract from SAP system. Copyright SAP SE.