Q: How to modify an invoice in quickbooks using qbxml and qbsdk13? This is my QBXML request 
<?xml version="1.0" ?>
<?qbxml version="6.0"?>
<QBXML>
    <QBXMLMsgsRq onError="stopOnError">
        <InvoiceModRq requestID="1">
            <InvoiceMod>
                <TxnID>85-1442639879</TxnID>
                <EditSequence>1442639879</EditSequence>
                <CustomerRef>
                    <ListID>80000005-1442639850</ListID>
                    <FullName>Bruce Banner</FullName>
                </CustomerRef>
                <TxnDate>2015-09-19</TxnDate>
                <RefNumber>5462</RefNumber>
                <InvoiceLineMod>
                    <ItemRef>
                        <ListID>8000000A-1442469770</ListID>
                        <FullName>Item 1</FullName>
                    </ItemRef>
                    <Quantity>1</Quantity>
                    <Rate>1100.00</Rate>
                </InvoiceLineMod>
            </InvoiceMod>
        </InvoiceModRq>
    </QBXMLMsgsRq>
</QBXML>

I am getting an error 
QuickBooks found an error when parsing the provided XML text stream.
please help

A: If you refer to the QuickBooks OSR: 


*

*https://developer-static.intuit.com/qbSDK-current/Common/newOSR/index.html
You'll notice that within the <InvoiceLineMod> element, this node is required: 


*

*<TxnLineID>
The OSR gives you a bit more information too: 

TxnLineID
Identification number of the transaction line. (TxnLineID
  is supported as of v2.0 of the SDK. With qbXML v1.0 and v1.1,
  TxnLineID is always returned as zero.) 
If you need to add a new transaction line in a transaction Mod
  request, you can do so by setting the TxnLineID to -1.

So, you'll need to add in a <TxnLineID> node. If it's a new line item, put -1 for the content within the node. If it's an existing line you're trying to update, put the TxnLineID value of the existing line in there. 
Example:
...
<InvoiceLineMod>
    <TxnLineID>-1</TxnLineID>
    <ItemRef>
        <ListID>8000000A-1442469770</ListID>
        <FullName>Item 1</FullName>
    </ItemRef>
    <Quantity>1</Quantity>
    <Rate>1100.00</Rate>
</InvoiceLineMod>
...

