All requests made against the Pulse API must be validated with an API Key.
Generate a new API Key in your Pulse account and copy/paste it when you add the sensors on vpdchart.com.
If you consider buying one of these sensors, use the code VPDCHARTDOTCOM at checkout and get 5% discount.
You need to have an account at https://console.ubibot.com/. Create a "Read API Key" for a sensor, copy it on vpdchart.com together with the "Channel ID", when you add the sensor and you're good to go.