Hi @Tonya125 , did you manage to get it to work in the meantime? It's nice to offer a discount but it'd be better if the guest had the option to accept it too!
Sometimes it works to delete the cookies and browser history and then restart the browser, that's something you could suggest to your guest. I'd recommend getting in touch with CS as well but it'd be best if the guest would do so, since the problem is on their side.
I hope that helps!