XML : Authorize.net, charge credit card request gives error as A duplicate transaction has been submitted

I am new to Authorize.Net, I am implementing Authorize.Net PHP SDK to implement it. I am trying to charge a credit card but it is giving error as:

"A duplicate transaction has been submitted"

I read several articles, reference : https://community.developer.authorize.net/t5/Integration-and-Testing/Prevent-Duplicate-Transactions/td-p/20417.

where the solution mentioned that add x_duplicate_window = (of your own choice, maximum 28800 seconds) to your script. so I added it as follows:

  <createTransactionRequest xmlns="AnetApi/xml/v1/schema/AnetApiSchema.xsd">      <merchantAuthentication>          <name>              <![CDATA[API_LOGIN_ID]]>          </name>          <transactionKey>              <![CDATA[API_TRANSACTION_KEY]]>          </transactionKey>      </merchantAuthentication>      <refId>          <![CDATA[ref1465541052]]>      </refId>      <transactionRequest>          <transactionType>              <![CDATA[authCaptureTransaction]]>          </transactionType>          <amount>1</amount>          <payment>              <creditCard>                  <cardNumber>                      <![CDATA[4111111111111111]]>                  </cardNumber>                  <expirationDate>                      <![CDATA[1233]]>                  </expirationDate>              </creditCard>          </payment>          <order>              <description>                  <![CDATA[DESCRIPTION]]>              </description>          </order>      </transactionRequest>      <extraOptions><![CDATA[x_duplicate_window=0]]></extraOptions>  </createTransactionRequest>    

but it throws error as

E00003 : The element 'createTransactionRequest' in namespace 'AnetApi/xml/v1/schema/AnetApiSchema.xsd' has invalid child element 'extraOptions' in namespace 'AnetApi/xml/v1/schema/AnetApiSchema.xsd'.

I am unable to add x_duplicate_window in my script. Is this the right way to prevent duplicate transaction error

NOTE: I'm working in sandbox environment and at LIVE mode

Please help.