Question about form-data

[metita]

Is there a brief tutorial on how to do a post request with form-data?

We tried several things, headers, post/get without success, we even tested through Postman and that worked flawlessly.

public fnTest(id){
    new GripJSONValue:data = grip_json_init_object();
    grip_json_object_set_string(data, "id", "1");
    grip_json_object_set_string(data, "email", "[email protected]");
    grip_json_object_set_string(data, "password", "testpw");

    new GripBody:body = grip_body_from_json(data);

    new GripRequestOptions:options = grip_create_default_options();
    //grip_options_add_header(options, "Content-Type", "application/json");
    //grip_options_add_header(options, "Content-Type", "multipart/form-data"); 
    grip_options_add_header(options, "User-Agent", "Grip");
    
    grip_request(
        "https://www.test.net/vinc.php", 
        body, 
        GripRequestTypePost, 
        "handlerTest", 
        options,
        id
    );
    grip_destroy_json_value(data);
    grip_destroy_body(body);
    grip_destroy_options(options);
}  

Are we doing something wrong? Content-Type form-data seems to be the only one with problems, any other post/get request works without problems.