Using the Google Maps API to draw radiuses

Hi

I'm trying to get a raduis circle working in google maps to show the area that my business covers.

I'm using the following link

http://www.dankross.co.uk/2015/04/using-the-google-maps-api-to-draw-radius-circles/

But it's not working. Does anyone know of a good plugin that will work or why it's not working?

Cheers
Kieran