Hybris commerce / C4C integration - communication failure

We had setup a data hub on a standalone tomcat. With this we try to integrate hybris commerce with C4C. If the data hub initiate a connection to the C4C tenant we get a connection timeout. If we intercept the communication with a proxy (portswigger / burp) we can see that the answer from C4C is a "500 - internal server error" with the header information "x-sap-icm-err-id: ICMENOSYSTEMFOUND" and a html page with the title "SAP Business Cloud for Customer - Currently not available".

In the C4C tenant this communicaton attempts are not logged in "Web service message monitoring".

If the send the same payload (xml-data) with the same header information (Content-type, User-agent, Authorization, SOAPaction) to the same URL (https://xxxxxxxx.crm.ondemand.com/sap/bc/srt/scs/sap/businesspartnerreplicationin?MessageId=D4B9E41A-8418-4C25-A952-CA41701FE263) from a RESTClient (Firefox addon) it works, we get a "202 accepted" and the customer is created in C4C.

What is the problem in the communication done by data hub (apache cxf)?

Do we need to configure apache cxf. We have setup the data hub as described in the installation guide.