Has some someone already got some luck by sending POST request in XML. The only thing I find on the forum is that it is not possible. Maybe someone has experience with passing it first to a third party (postman) before sending it to the API?
I don’t know why the first post say it was not possible but this is already possible since a long time. You need to select raw payload. However, some API may be harder to get it work. So provide url doc for the API you are trying to connect and maybe someone can have a look