Pay the fine ? Are you kidding ? They are asking for the full PCN penalty of £60, yet this is also the maximum penalty at the adjudicators, so it is a total no-brainer to take them to London Tribunals where your case is very strong, because the penalty is fixed and there are no additional costs at all. In fact I would go so far as to say I bet they don't contest an appeal at LT. So bad is their case you would have a good argument for a costs application.