Hi Viktor,
I had our PI guys do the WebService configuration, once they said they're finished it all worked for me. In my case they created a custom Web service based on my requirements, then created a proxy to it, I hooked up the technical system, created and activated the Replication model in mdgimg (along with the outbound implementation). Created the filter in DRFF transaction and then when running DRFOUT it all worked and sent the XMLs to SXMB_MONI.
Perhaps you should make sure you have all the steps done. Easy thing to miss is the filter and the Replication model activation.
In our case it worked just fine.
Hope that helps,
Regards,
Boris