Combo chart axis legend

I am trying to use ChartBoot to produce a combo chart which in most respects it does fine. However, a small niggle, where I have a chart which has a percentage line overlaying columns the legend on the right axis (as I have set it up) shows the numbers of percentage e.g. 0 – 60 but it won’t show the format e.g. 0%, 30% etc. Works fine in Google. Any ideas much appreciated.

https://www.ads-software.com/plugins/chartboot-for-wordpress/