Sending multipart form data does not appear to work correctly - reactor-netty

Question

I'm trying to call an endpoint that accepts PUT requests and expects to be passed 3 different MultipartFile paramters. Let's call them A, B and C.
When I make a request to the same enpoint from Postman it works as intended. When I do it via the the reactor-netty lib I get back Error 400 Bad Request:
"Required request part 'A' is not present"
HttpClient
.create()
// skipping baseUrl and headers headers
.put()
.uri(ENDPOINT_URI)
.sendForm((req, form) -> form
.multipart(true)
.file("A", FILE_A, "application/json)
.file("B", FILE_B, "application/json)
.file("C", FILE_C, "application/json))
.response()
I could not find much info online to establish if this is the best way to achieve what I need. Can you please point me to where I'm going wrong or perhaps towards an alternative solution?
Thanks

Answer 1

After looking throught the source of the HttpClientForm (the class in which .file is called) I found this:
default HttpClientForm file(String name, InputStream stream, #Nullable String contentType) {
return file(name, "", stream, contentType);
}
as well as this:
default HttpClientForm file(String name, File file, #Nullable String contentType) {
return file(name, file.getName(), file, contentType);
}
Somehow I thought that the first paramter 'name' is the one that is matched with the #RequestParam value. By the looks of it its actually the second.
Also if using an input stream instead of a File I had to call the the file method with 4 paramters and pass the name explicitly as the second parameter like so:
file(name, "A", stream, contentType)