To be able to record TNT PPV you have to book it from the Sky remote. If you do it online or they do it for you via the call centre then you'll need to watch it live or watch the catch-up which is repeated multiple times throughout the week. Your PPV payment entitles you to watch them as often as you want while they're up for viewing.
If it doesn't allow you to use the remote then it's possible that you have an unpaid previous event and you need to call them to resolve that first. While there, once your account is up to date, ask them to turn off the PPV entitlement and back on. This will tell the Sky box you are entitled to make a booking. It's a glitch from the BT PPV days.
Edit: obviously, once updated make sure you use the remote to book it, it may not be instant so don't shout at the agent if not.
