Do not use the element &1 in the association definition.

What causes this issue?

In the consumption CDS view, a path expression that is closed using an
element is used in the association definition. This is not allowed.

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?

Remove the path expression that is closed using an element from the
association definition in the 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.