The approach you're using to set the Content-Type header is correct in principle. Writing to the "HttpHeaders" context property should allow you to set custom HTTP headers. However, there are a few potential issues that could prevent this from working:

a. The property name "HttpHeaders" is case-sensitive. Make sure it's exactly as shown.

b. The namespace URI must be correct. The one you're using looks right, but double-check it.

c. The format of the header string is important. Each header should be on a separate line, ending with a CRLF (\r\n).

Another approach is to set these properties in the WCF-Custom adapter configuration:

• In the send port configuration, go to the "Messages" tab. Set "Message body" to "Raw". Set "Content type" to "application/soap+xml". In the "Outbound HTTP headers" section, add a new header: Name: SOAPAction Value: actioname