Hi Michiel,
Just putting it in an anwswer since it is not accepting my tagged message. I've looked at the topic you suggested, but my issue is that i cant override the xmime:content-type. My request (as the debug in webservices gives it, is like:
<soapenv:Body>
<ns5:UploadDocumentRequest xmlns:xmime="http://www.w3.org/2005/05/xmlmime">
<ns5:XmlFile>binarycontent</ns5:XmlFile>
<ns5:AttachmentFile xmime:contentType="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet">binarycontent</ns5:AttachmentFile>
</ns5:UploadDocumentRequest>
</soapenv:Body>
But it looks like it is still posted as content-stream: application/octet-stream
Pretty strange
BR,
Mike
Can you attach the WSDL of the webservice?
In an other question this seems to be caused by the wsdl:
https://forum.mendix.com/link/questions/86029
(It's about using xmime:base64Binary instead of xs:base64Binary)