UFFE Invoice

I want the following:

When adding a new invoice, I want an automatic export of this invoice to a xml file.

What I tried and works:

I've made a Universal Function, based on UFFE. 

File is created. But filename is wrong and the xml (0.xml) is not filled correctly.

Filepath = C:\Users\#####\Temp\DocKey@.xml

Line Source:

SELECT "DocNum", "CardCode", "CardName" FROM OINV WHERE "DocNum" = $[$8.0.NUMBER]

Body

#foreach (@line in @DocumentLines)
#BEGIN
@line.Get('DocNum')
#END

Can someone push me in the right direction?