Join &1 is not allowed.

What causes this issue?

A join is used in the SELECT statement in the consumption CDS view. 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 join in the consumption CDS view. You can use an association
instead.

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.