User defined function in xsl

  I have have customized an xsl file for Payament module.

I created a user defined function but get the following message:

Caused by: oracle.xdo.parser.v2.XPathException: Namespace prefix 'myfunctionname' used not declard.

Here's an exerpt of the code. Not sure if this is the way to do it. Also, I changed the version from 1.0 to 2.0 as the devlopers guide seems to indicate this is possible

<?xml version="2.0" encoding="UTF-8"?>

<!--  $Header: XX_IBY_SEPA.xsl 120.0.12000000.28 2012/10/23 10:02:27 asarada noship $   --> 

<!--  dbdrv: exec java oracle/apps/xdo/oa/util XDOLoader.class java &phase=dat checkfile:~PROD:patch/115/publisher/templates:IBY_SEPA.xsl UPLOAD -DB_USERNAME &un_apps -DB_PASSWORD &pw_apps -JDBC_CONNECTION &jdbc_db_addr -LOB_TYPE TEMPLATE -APPS_SHORT_NAME IBY -LOB_CODE IBY_SEPA_CREDIT_INIT_TEMPLATE -LANGUAGE en -XDO_FILE_TYPE XSL-XML -FILE_NAME &fullpath:~PROD:patch/115/publisher/templates:IBY_SEPA.xsl -->