Works for me with a random test. The 10% discount is added at the checkout:

1. Did you book using the URL on the benefits portal?
2. If that link doesn't work for you, then what tour are trying to book on which date and time?

With these discount offers it is always worth checking out what other offers or prices are available as it may be cheaper by other means.

With the example @rvdborgt gave, as well as most main attractions in London, for 2 people the 2for1 offer with rail tickets will be cheaper even with purchasing a paper rail ticket to qualify for it.

https://www.daysoutguide.co.uk/2for1-london