% Store the channel ID for the range sensor channel.
channelID = *******;

% Provide the ThingSpeak alerts API key.

alertApiKey = 'TAK*****************';

% Set the address for the HTTTP call
alertUrl="https://api.thingspeak.com/alerts/send";

% webwrite uses weboptions to add required headers.  Alerts needs a ThingSpeak-Alerts-API-Key header.
options = weboptions("HeaderFields", ["ThingSpeak-Alerts-API-Key", alertApiKey ]);

% Set the email subject.
alertSubject = sprintf("Salt level status");

% Read the recent data.
saltData = thingSpeakRead(channelID,'NumPoints',1,'Fields',1);

% Get the most recent point in the array of salt data.
    lastValue = saltData(end); 

    % Set the outgoing message when level greater than 400
    if (lastValue>400)
        alertBody = ' I need salt! '    
    end
   try
    webwrite(alertUrl , "body", alertBody, "subject", alertSubject, options);

  catch someException
   fprintf("Failed to send alert: %s\n", someException.message);
   end