You are trying to update the value of the 'Originating Template' using the REST API, but the value does not get updated even after your PATCH request succeeds (200).
Any Clarity supported release.
'Originating Template' is a read-only attribute that is meant to point to the Template from which this investment was created, if any.
If you need to point to a Template for a different use case, you can create a new attribute instead.