Hi Pavan,
I tried adding this line in the payload starting but it failed.
<?xml version="1.0" encoding="UTF-8"?>
<atom:entry xmlns:atom="http://www.w3.org/2005/Atom"
xmlns="http://www.w3.org/2005/Atom"
xmlns:m="http://schemas.microsoft.com/ado/2007/08/dataservices/metadata"
xmlns:d="http://schemas.microsoft.com/ado/2007/08/dataservices">
<id>http://hostname:portname/sap/opu/odata/sap/ZSALESORDER_SRV/SO_HEADERS</id>
<title type="text">SO_HEADERS</title>
<updated>2015-07-21T06:46:49Z</updated>
<author>
<name/>
</author>
<link href="SO_HEADERS" rel="self" title="SO_HEADERS"/>
<entry>
<id>http://hostname:portname/sap/opu/odata/sap/ZSALESORDER_SRV/SO_HEADERS('4970')</id>
<title type="text">SO_HEADERS('4970')</title>
<updated>2015-07-21T06:46:49Z</updated>
<category term="ZSALESORDER_SRV.SO_HEADER" scheme="http://schemas.microsoft.com/ado/2007/08/dataservices/scheme"/>
<link href="SO_HEADERS('4970')" rel="edit" title="SO_HEADER"/>
<link href="SO_HEADERS('4970')/SO_ITEMSet" rel="http://schemas.microsoft.com/ado/2007/08/dataservices/related/SO_ITEMSet" type="application/atom+xml;type=feed" title="SO_ITEMSet">
<m:inline>
<feed xml:base="http://hostname:portname/sap/opu/odata/sap/ZSALESORDER_SRV/">
<id>http://hostname:portname/sap/opu/odata/sap/ZSALESORDER_SRV/SO_HEADERS('4970')/SO_ITEMSet</id>
<title type="text">SO_ITEMS</title>
<updated>2015-07-21T06:46:49Z</updated>
<author>
<name/>
</author>
<link href="SO_HEADERS('4970')/SO_ITEMSet" rel="self" title="SO_ITEMS"/>
<entry>
<id>http://hostname:portname/sap/opu/odata/sap/ZSALESORDER_SRV/SO_ITEMS(SO_ID='4970',ITEM_NO='000010')</id>
<title type="text">SO_ITEMS(SO_ID='4970',ITEM_NO='000010')</title>
<updated>2015-07-21T06:46:49Z</updated>
<category term="ZSALESORDER_SRV.SO_ITEM" scheme="http://schemas.microsoft.com/ado/2007/08/dataservices/scheme"/>
<link href="SO_ITEMS(SO_ID='4970',ITEM_NO='000010')" rel="edit" title="SO_ITEM"/>
<content type="application/xml">
<m:properties>
<d:SO_ID>0</d:SO_ID>
<d:ITEM_NO>10</d:ITEM_NO>
<d:MAT_NO>100-100</d:MAT_NO>
<d:PLANT>1000</d:PLANT>
<d:TARGET_QTY>4</d:TARGET_QTY>
<d:TARGET_QU>ST</d:TARGET_QU>
<d:ITEM_CATEG>TAN</d:ITEM_CATEG>
<d:PURCH_NO_C>TEST ORDER</d:PURCH_NO_C>
<d:PURCH_DATE>20150728</d:PURCH_DATE>
<d:INCOTERMS1>CIP</d:INCOTERMS1>
<d:INCOTERMS2>Nürnberg</d:INCOTERMS2>
<d:PMNTTRMS>ZB01</d:PMNTTRMS>
<d:PRICE_DATE>20150721</d:PRICE_DATE>
<d:SALES_UNIT>ST</d:SALES_UNIT>
<d:DIVISION>00</d:DIVISION>
<d:CURRENCY>EUR</d:CURRENCY>
</m:properties>
</content>
</entry>
<entry>
<id>http://hostname:portname/sap/opu/odata/sap/ZSALESORDER_SRV/SO_ITEMS(SO_ID='4970',ITEM_NO='000020')</id>
<title type="text">SO_ITEMS(SO_ID='4970',ITEM_NO='000020')</title>
<updated>2015-07-21T06:46:49Z</updated>
<category term="ZSALESORDER_SRV.SO_ITEM" scheme="http://schemas.microsoft.com/ado/2007/08/dataservices/scheme"/>
<link href="SO_ITEMS(SO_ID='4970',ITEM_NO='000020')" rel="edit" title="SO_ITEM"/>
<content type="application/xml">
<m:properties>
<d:SO_ID>0</d:SO_ID>
<d:ITEM_NO>20</d:ITEM_NO>
<d:MAT_NO>100-100</d:MAT_NO>
<d:PLANT>1000</d:PLANT>
<d:TARGET_QTY>3</d:TARGET_QTY>
<d:TARGET_QU>ST</d:TARGET_QU>
<d:ITEM_CATEG>TAN</d:ITEM_CATEG>
<d:PURCH_NO_C>TEST ORDER</d:PURCH_NO_C>
<d:PURCH_DATE>20150728</d:PURCH_DATE>
<d:INCOTERMS1>CIP</d:INCOTERMS1>
<d:INCOTERMS2>Nürnberg</d:INCOTERMS2>
<d:PMNTTRMS>ZB01</d:PMNTTRMS>
<d:PRICE_DATE>20150721</d:PRICE_DATE>
<d:SALES_UNIT>ST</d:SALES_UNIT>
<d:DIVISION>00</d:DIVISION>
<d:CURRENCY>EUR</d:CURRENCY>
</m:properties>
</content>
</entry>
<entry>
<id>http://hostname:portname/sap/opu/odata/sap/ZSALESORDER_SRV/SO_ITEMS(SO_ID='4970',ITEM_NO='000030')</id>
<title type="text">SO_ITEMS(SO_ID='4970',ITEM_NO='000030')</title>
<updated>2015-07-21T06:46:49Z</updated>
<category term="ZSALESORDER_SRV.SO_ITEM" scheme="http://schemas.microsoft.com/ado/2007/08/dataservices/scheme"/>
<link href="SO_ITEMS(SO_ID='4970',ITEM_NO='000030')" rel="edit" title="SO_ITEM"/>
<content type="application/xml">
<m:properties>
<d:SO_ID>0</d:SO_ID>
<d:ITEM_NO>30</d:ITEM_NO>
<d:MAT_NO>100-100</d:MAT_NO>
<d:PLANT>1000</d:PLANT>
<d:TARGET_QTY>2</d:TARGET_QTY>
<d:TARGET_QU>ST</d:TARGET_QU>
<d:ITEM_CATEG>TAN</d:ITEM_CATEG>
<d:PURCH_NO_C>TEST ORDER</d:PURCH_NO_C>
<d:PURCH_DATE>20150728</d:PURCH_DATE>
<d:INCOTERMS1>CIP</d:INCOTERMS1>
<d:INCOTERMS2>Nürnberg</d:INCOTERMS2>
<d:PMNTTRMS>ZB01</d:PMNTTRMS>
<d:PRICE_DATE>20150721</d:PRICE_DATE>
<d:SALES_UNIT>ST</d:SALES_UNIT>
<d:DIVISION>00</d:DIVISION>
<d:CURRENCY>EUR</d:CURRENCY>
</m:properties>
</content>
</entry>
<entry>
<id>http://hostname:portname/sap/opu/odata/sap/ZSALESORDER_SRV/SO_ITEMS(SO_ID='4970',ITEM_NO='000040')</id>
<title type="text">SO_ITEMS(SO_ID='4970',ITEM_NO='000040')</title>
<updated>2015-07-21T06:46:49Z</updated>
<category term="ZSALESORDER_SRV.SO_ITEM" scheme="http://schemas.microsoft.com/ado/2007/08/dataservices/scheme"/>
<link href="SO_ITEMS(SO_ID='4970',ITEM_NO='000040')" rel="edit" title="SO_ITEM"/>
<content type="application/xml">
<m:properties>
<d:SO_ID>0</d:SO_ID>
<d:ITEM_NO>40</d:ITEM_NO>
<d:MAT_NO>100-100</d:MAT_NO>
<d:PLANT>1000</d:PLANT>
<d:TARGET_QTY>1</d:TARGET_QTY>
<d:TARGET_QU>ST</d:TARGET_QU>
<d:ITEM_CATEG>TAN</d:ITEM_CATEG>
<d:PURCH_NO_C>TEST ORDER</d:PURCH_NO_C>
<d:PURCH_DATE>20150728</d:PURCH_DATE>
<d:INCOTERMS1>CIP</d:INCOTERMS1>
<d:INCOTERMS2>Nürnberg</d:INCOTERMS2>
<d:PMNTTRMS>ZB01</d:PMNTTRMS>
<d:PRICE_DATE>20150721</d:PRICE_DATE>
<d:SALES_UNIT>ST</d:SALES_UNIT>
<d:DIVISION>00</d:DIVISION>
<d:CURRENCY>EUR</d:CURRENCY>
</m:properties>
</content>
</entry>
</feed>
</m:inline>
</link>
<link href="SO_HEADERS('4970')/$links/SO_ITEMSet" rel="http://schemas.microsoft.com/ado/2007/08/dataservices/relatedlinks/SO_ITEMSet" type="application/xml" title="SO_ITEMSet"/>
<content type="application/xml">
<m:properties>
<d:SO_ID>0</d:SO_ID>
<d:CURRENCY>EUR</d:CURRENCY>
<d:DOC_TYPE>OR</d:DOC_TYPE>
<d:DOC_DATE>20150721</d:DOC_DATE>
<d:SALES_ORG>1000</d:SALES_ORG>
<d:DIST_CHANNEL>10</d:DIST_CHANNEL>
<d:DIVISION>00</d:DIVISION>
<d:SALES_GRP>130</d:SALES_GRP>
<d:SALES_OFF>1030</d:SALES_OFF>
<d:REQ_DATE_H m:null="true"/>
<d:PURCH_DATE m:null="true"/>
<d:INCOTERMS1>CIP</d:INCOTERMS1>
<d:INCOTERMS2>Nürnberg</d:INCOTERMS2>
<d:PMNTTRMS>ZB01</d:PMNTTRMS>
<d:PRICE_DATE>20150721</d:PRICE_DATE>
<d:PURCH_NO_C>TEST ORDER</d:PURCH_NO_C>
</m:properties>
</content>
</entry>
</atom:entry>