Today's date & days before planned delivery date

What causes this issue?

The delivery date agreed in the purchase order is in the future.

System Response

The system has determined that the product <ZG>(planned delivery date
- current date) * amount of the invoice item</> is greater than the
tolerance for schedule deviation set in the Customizing system.
When you post the invoice, the system blocks it for payment with the
blocking reason "schedule variance".

Error message extract from SAP system. Copyright SAP SE.