Their letter re-offers the discount, so you can either pay this, or register an appeal at London Tribunals.The letter gives you a verification code to use if you want to do this.
There was a previously successful case at this location, 2220554800. This succeeded on the basis of inadequate signage. Whether any improvements have been made I can't tell you but you could have a look on GSV to see if they have a later view than 2022.
Paying closes the matter, needless to say, and you join the Mugged Club ! It all depends on how annoyed you are to risk the extra cost of going to London Tribunals.