Error 401 Matlab Analysis | ThingSpeak Apps | Forum

I am trying to use this app to clean the channels, I found this code:

ChannelID = "MY Channel
I've already changed it"
UserAPIKey = "My API
I've already changed it"
url = sprintf('https://api.thingspeak.com/channels/%s/feeds.json?api_key=%s',num2str(ChannelID),UserAPIKey)
response = webwrite(url, weboptions('RequestMethod','delete'))

Which supposedly does but at the time of making it work gives me the following error:

Error using matlab.internal.webservices.HTTPConnector/copyContentToByteArray (line 373)
The server returned the status 401 with message "" in response to the request to URL https://api.thingspeak.com/channels/....

Error in readContentFromWebService (line 46)
byteArray = copyContentToByteArray(connection);

Error in webwrite (line 139)
[varargout{1:nargout}] = readContentFromWebService(connection, options);

Error in Custom (no starter code) 1 (line 4)
response = webwrite(url, weboptions('RequestMethod','delete'))

My channel is public, so it should not be due to any access restriction.