buy X get Y free is not working

I have problems to get it working. I have read a lot about it and think i have put all the things right but nothings working.
I have the one page check out module. The site is www.salomobikes.nl

And i have made a test coupon for article Rider20E 4718251590886

thanks!

Hello,

Can you type out the details of your coupon setup?