The target of the composition association &1 must be a consumption view.

What causes this issue?

Within a transactional consumption CDS view, it is only possible to
define a composition association to an item view that is also a
transactional consumption CDS view. The item view may not be a
transactional CDS view.

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?

Create a transactional consumption CDS view based on the transactional
view that can be used for a composition association within the
transactional consumption CDS view.

Procedure for System Administrators

Contact the corresponding developer of the CDS view to correct the
error.

Error message extract from SAP system. Copyright SAP SE.