I'm using a Call web service action to try and copy a document set from Site Collection A to Site Collection B. I haven't been able to find anything online to help me along, so I started at a more basic level and just trying to copy a document from A/Documents/DocumentSet to B/Documents/DocumentSet.
I'm using copy.asmx and the CopyIntoItems method and I can copy a document into the root but haven't been able to get the destination URL right to allow me to copy the document into the Document Set. I get the following error:
<CopyResult ErrorCode="Unknown" ErrorMessage="Object reference not set to an instance of an object." DestinationUrl="http://vspiappweb02dv:9292/sites/Board/AgendaDocs/Board%20of%20Directors%20-%20February%2C%202016%C2..." />
If I copy it to the library root I get:
<CopyResult ErrorCode="Success" DestinationUrl="http://vspiappweb02dv:9292/sites/Board/AgendaDocs/Non-Procurement%20Resolution%20Agenda%20Report.doc..." />
This seems to be your scenario Nintex Workflow - Move Documents and Preserve Version History - Vadim Tabakman
Where he is moving a document from one Doc Set to another and preserving history using the Author.dll features in SP on prem. Otherwise you can use the actions
Copy to SharePoint, or
Call Web Service -> Copy.asmx
Hope that helps!