How can I debug 400-type error messages from "webread" and "webwrite" in MATLAB R2024b?

I am trying to send a request to a website with the "webwrite" command and capture the output. The website should receive the request and send back a payload of data, but I am getting a vague error that does not help me figure out why I can't access the site.
The error I am seeing is "The server returned the status 403 with message "Forbidden" in response to the request to URL". I can access the site perfectly fine through a browser and outside of MATLAB, so I don't know why I am getting this error when using "webread" in MATLAB.

Answer 1

[MathWorks Support Team]

When a website returns a 400 type response to a function like "webread" or "webwrite", there is often some additional data that is sent in the response that is not displayed in the output of the function. This information usually provides a bit of context regarding why the request received that type of response.

To capture the body of the response output, you can use a matlab.net.http.RequestMessage object. You can then inspect the response when sending the request, which will capture the body of the HTTP response instead of showing an error message.

req = matlab.net.http.RequestMessage
req.Method = matlab.net.http.RequestMethod.GET

response = send(req, <url>)

% inspect response.Body.Data

Answer 2

[Richard Zapor]

A slight variation when sending a JSON string to a site to get a response and catching the error if a 400 event happens

options=weboptions('MediaType', 'application/json');
try
    response=webwrite(url,JSON_string,options)
catch
    import matlab.net.http.*
    body=JSON_string;
    r=RequestMessage('POST',[],body);
    resp=r.send(url);
    show(resp)
    resp.Body.Data
end