CURLMBS (RestAPI and MultipartFormData)

I have a problem very similar to the one described here:
(Restful API).

especially for MultipartFormData with Json.

Following that thread, I saw that @Tim_Parnell helped the topic creator a lot, with URLConnection.

Since I generally use CURLMBS, how can I configure it in a case similar to the one I mentioned above (restful api)?

Thank you.

You can use FormAdd and FormFinish methods in CURLSMBS class to assemble multipart form posts.

should I build the json object field by field?
or, if I can pass a single string containing the entire json, what is the syntax, among many options of CURLSMBS class?
can you write a snippet here?

Well, you normally use multi part if you have to upload multiple things.
e.g. a JSON for an API parameter and then attachments like an image to upload.

I was saying at the beginning that my situation is similar to the topic I mentioned.

the body of the request is Json type, but it must be transformed (in that case, I saw, with URLConnection, via a module prepared by @Björn_Eiríksson and then modified by @Tim_Parnell).

I was asking how I could do that with CURLSMBS.

if you confirm that the solution is FormAdd, could you add some details?