See the remarks for this method https://www.revitapidocs.com/2023/548c4181-2779-40a2-8276-b7a43a85a161.htm
Also could be the original crop/split has to be removed first.
And there could be a number of other things blocking it.
First; Is it in the UI possible to set that shape for that view, if not then it's also not possible in the API
