Similar to this deal.
The purple box looks the same as last time, so the same steps/methods may apply.
I got the purple pop up box when I was checking out. I've tried logged out and logged in, as well as creating a new account and managed to get the box all three times, so I don't think it's targeted. YMMV.
The expiry has changed since last time, making the voucher valid only for the day.
I just logged in and out added things to cart to order and no popup at all.