https://api.stackexchange.com/2.2/comments/{id}/flags/add?key={key}&site=stackoverflow&access_token={token}&option_id=33790

{error_id: 404, error_message: "this method cannot be called this way", error_name: "no_method"}
error_id
:
404
error_message
:
"this method cannot be called this way"
error_name
:
"no_method"

var url_add = "https://api.stackexchange.com/2.2/comments/{id}/flags/add";
var payload =  {site: 'stackoverflow', id: id, option_id: flag_option, key: Key, access_token: token, filter: 'default', preview:true};
$.post(url, payload, 'json').done(function(data) {
       console.log(data);
});