You can’t submit both a Request Body and form url encoded parameters.
Can you change the parameter content type to JSON?
Otherwise this thread showing how to remove the body may help:
All [Api*] attributes are just metadata annotations, they do not have any impact to your Services implementation. You still need to do your own validation.
after making changes I got what I wanted, but now changed content-type before was json and therefore the request is not worked out, how to make so that content-type remained json?