Quiz - on passing not opening up a URL

I have a quiz (pulling all 10 questions from a pool) built in Cp 8 where on passing the user is presented with a well done slide then they are asked to click a button which should direct them to an internal URL.  It is not working.

I have tried a click box, a button (it will go to another slide but not open a URL), i have tried 'on enter' open URL on this second slide, i have tried advanced actions (on achieving ## points go to URL) but nothing seems to open the URL.  When i Preview the last slide in the quiz it opens the URL, when i publish the quiz it does not, i have added in quiz preferences on passing go to URL, no joy - frustrating

Please note i have not 'enabled reporting' option as I will not be reporting results all the user has to do is pass the quiz and visit the URL on passing.

Am i asking the quiz to do something it just cannot do?

Any advice welcome - thank you jo