Using the Nintex Workflows for Office 365 REST API

Hi, 

I am having trouble trying to use the "Import into new workflow" operation available in the O365 REST API for Nintex Workflows.

SDK documentation does not give much details, in particular about the way to send the nwp content in the request's body. All my attempts fail with a "NW-1001 - The specified package is not valid." error

Has anyone already done this ?

Thanks,