I have read every post regarding my problem and tested the transformation with https://www.freeformatter.com/xpath-tester.html but found no solution to the error so far.
the goal is to read relevant values from my photovoltaik-system.
http:///measurements.xml
[ab.binding.http.internal.HttpBinding] - Transformation 'XPATH(//Measurement[@Type='GridInjectedPower']/number(@Value))' threw an exception. [response=<?xml version='1.0' encoding='UTF-8'?><root><Device Name='PIKO 3.0-2 MP plus' Type='Inverter' Platform='Net16' HmiPlatform='HMI17' NominalPower='3000' UserPowerLimit='nan' CountryPowerLimit='nan' Serial='763968EG006880310021' OEMSerial='10351315' BusAddress='1' NetBiosName='INV006880310021' WebPortal='PIKO Solar Portal' ManufacturerURL='kostal-solar-electric.com' IpAddress='192.168.211.10' DateTime='2020-07-28T11:19:40' MilliSeconds='083'><Measurements><Measurement Value='234.1' Unit='V' Type='AC_Voltage'/><Measurement Value='11.940' Unit='A' Type='AC_Current'/><Measurement Value='2798.0' Unit='W' Type='AC_Power'/><Measurement Value='2794.4' Unit='W' Type='AC_Power_fast'/><Measurement Value='49.996' Unit='Hz' Type='AC_Frequency'/><Measurement Value='301.2' Unit='V' Type='DC_Voltage'/><Measurement Value='9.208' Unit='A' Type='DC_Current'/><Measurement Value='420.7' Unit='V' Type='LINK_Voltage'/><Measurement Value='2467.1' Unit='W' Type='GridPower'/><Measurement Value='0.0' Unit='W' Type='GridConsumedPower'/><Measurement Value='2467.1' Unit='W' Type='GridInjectedPower'/><Measurement Value='330.9' Unit='W' Type='OwnConsumedPower'/><Measurement Value='100.0' Unit='%' Type='Derating'/></Measurements></Device></root>]
org.openhab.core.transform.TransformationException: transformation throws exceptions
at org.openhab.core.transform.TransformationHelper$TransformationServiceDelegate.transform(TransformationHelper.java:71) ~[bundleFile:?]