The attached xml is an example found on this site, as would be the structure of this xml for a return, transaction type = 4, considering that the merchandise is returned to available.
<eConnect xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<SOPTransactionType>
<eConnectProcessInfo xsi:nil="true"/>
<taSopLineIvcInsert_Items>
<taSopLineIvcInsert>
<SOPTYPE>3</SOPTYPE>
<ITEMNMBR>COMPBOOK</ITEMNMBR>
<QUANTITY>2</QUANTITY>
<CUSTNMBR>AARONFIT0001</CUSTNMBR>
<DOCDATE>4/1/2010</DOCDATE>
<LOCNCODE>WAREHOUSE</LOCNCODE>
<DEFPRICING>1</DEFPRICING>
</taSopLineIvcInsert>
</taSopLineIvcInsert_Items>
<taSopHdrIvcInsert>
<SOPTYPE>3</SOPTYPE>
<DOCID>STDINV</DOCID>
<CUSTNMBR>AARONFIT0001</CUSTNMBR>
<BACHNUMB>TESTBATCH</BACHNUMB>
<DOCDATE>02/04/2011</DOCDATE>
<LOCNCODE>WAREHOUSE</LOCNCODE>
<DEFPRICING>1</DEFPRICING>
<CREATETAXES>1</CREATETAXES>
<DEFTAXSCHDS>1</DEFTAXSCHDS>
</taSopHdrIvcInsert> </SOPTransactionType>
</eConnect>