Hi @Anonymous User
I don't buy or use NowTV Sports Passes myself or use my PC with the NowTV Player software on their website.
Where the only PIN codes that i am aware of is a four digit PIN code that you can setup on your account to avoid buying passes or a Parental PIN.
Not aware of entering a PIN when you have already purchased a pass and trying to watch any of the Sky Sports channels.
Nowtv have introduced a mandatory PIN when accessing Live Movies, but not live Sports from what i am aware of.
You can find these two PIN settings under My Account > Settings & PIN's whilst logged in on here.
Maybe have a word with live chat to see if they can help you out.
Link here to live chat.