Save XML to CSV using java Namespace prefix is undeclared

Question

I am trying to save XML file to CSV with java, but I receive 'Namespace prefix 'lst' is undeclared' error message.

This is XSL file:

<xsl:stylesheet version="1.0" 
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="text" encoding="UTF-8"/>

<xsl:template match="/listInvoice">
    <!-- header -->
    <xsl:text>nieco&#10;</xsl:text>
    <!-- data -->
    <xsl:for-each select="lst:invoice/inv:invoiceHeader">
        <!-- classroom data -->
        <xsl:variable name="inv:invoiceHeader">
            <xsl:value-of select="@inv:id" />
            <xsl:text>,</xsl:text>

        </xsl:variable>

    </xsl:for-each>
</xsl:template>

</xsl:stylesheet>

This is XML file:

<?xml version="1.0" encoding="UTF-8"?>
<listInvoice>
  <lst:invoice>
    <inv:invoiceHeader>
      <inv:id>9136</inv:id>
      <inv:invoiceType>issuedInvoice</inv:invoiceType>
      <inv:number>
        <typ:id>435</typ:id>
        <typ:numberRequested>1710203</typ:numberRequested>
        </inv:number>
</inv:invoiceHeader>
 </lst:invoice>
  </listInvoice>  

java code:

import java.io.File;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.Result;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import javax.xml.transform.stream.StreamSource;

import org.w3c.dom.Document;

    class XMLtoCsVConversion2 {

        public static void main(String args[]) throws Exception {
            File stylesheet = new File("new.xsl");
            File xmlSource = new File("test.xml");

            DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
            DocumentBuilder builder = factory.newDocumentBuilder();
            Document document = builder.parse(xmlSource);

            StreamSource stylesource = new StreamSource(stylesheet);
            Transformer transformer = TransformerFactory.newInstance()
                    .newTransformer(stylesource);
            Source source = new DOMSource(document);
            Result outputTarget = new StreamResult(new File("xyz.csv"));
            transformer.transform(source, outputTarget);
        }
    }

Could you please help where could be the problem? Could be the reason be xml tag consist of 2 parts splitted by semicolon?

Thanks