If I delete the line with ZUST_AUSB then the node can parse the XML without errors. At first glance, the problem is that the node isn’t differentiating between the lines with “ZUSTAUSB” and “ZUST_AUSB” - it’s somehow not picking up on the underscore character.
Also, just so by the way. For anyone who finds this in the future:
I was able to do a SOAP request using the normal POST node, just like a REST service.
You can put the XML as a column in the request body. It’s just picky about encoding, a “Content-Type: application/soap+xml; charset=utf-8” header solved that for me, binary to text to make it readable.