Answer
Check the exact action name and path against the projection's actual metadata rather than guessing based on the client-visible command name — the real bound action for releasing a Customer Order is CustomerOrderSet(OrderNo='order_no')/IfsApp.CustomerOrderHandling.CustomerOrder.SetReleased, not a ReleaseOrder-named action. Also double-check how you're setting the If-Match/ETag header for the call — the raw W/"..." ETag value needs to go in as an actual header value, not with its quote characters HTML-entity-encoded (") as literal text inside the header, which produces a different kind of failure than simply using the wrong action name.