Source &1 &2 is service-related but target &3 &4 is not

What causes this issue?

The source item is marked for service-related revenue recognition, so
that revenues are recognized in the target item when the billing
document is created. This is the standard setting.

System Response

This message is for information purposes only. The target item does not
influence the revenue recognition process and therefore does not
influence the source item.

How to fix this error?

Check your copying control settings in Customizing for the source to
target document. Ensure that the required revenue recognition process
works for both items. In other words:
Are the document types and item categories properly maintained?
Has the correct revenue recognition category been assigned to the item
categories?

Error message extract from SAP system. Copyright SAP SE.