Thanks for your posting and using Aspose.Cells for Cloud.
Please see the help relating to all REST URIs from the following link.
( https://apireference.aspose.cloud/cells/ )
and this is the help of Smart Marker related URI
( https://apireference.aspose.cloud/cells/#/Workbook/PutWorkbookCreate )
The smart marker URI is
Smart marker processing result.
It expect xml file path in the URI itself and it means xml file itself be inside the storage space.
Both approaches are right, if you will not specify the xml file path, then you will have to specify it inside the body.
This documentation article shows it how to make use of this API. In this article, you will also be able to download the Designer Spreadsheet and see the XML used to specify data.
( http://www.aspose.com/docs/display/cellscloud/smartMarker )