Hello Sanjay
You can find the details about the XML schema for customer Invoice Request upload in the following link.
Inbound Service Interface (public)
You may also refer to the additional resources in the Business Center.
https://wiki.sme.sap.com/wiki/display/OnDemandWiki/Archive
Here you can get the excel file to be used and also the typical structure of the XML file.There is also PDF explaining the full process “File Upload of Invoice Requests”.
Hope this helps.
Thanks
Parveen