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

What causes this issue?

The source is a service-related revenue recogntion item but the target
is a time-related revenue recognition item. In service-related revenue
recognition, the system uses the the services rendered, not the source
item, to determine the revenues that should be recognized. Normally an
item in the release order or in a delivery determines the revenue to be
recognized.

System Response

This message is for information purposes only. For revenue recognition,
the items are processed completely separately from each other. This
means that the target item is treated as a time-related revenue
recognition item independent of the source item. Determining factors
are the value and defined periods of the target item. All other items
do not influence the revenue recognition process.

How to fix this error?

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

Error message extract from SAP system. Copyright SAP SE.