Check your payment card details are up to date on your My Account > Payment Details page and that there is credit available on the card (even though you want a free trial).
Also if you've ever had a free trial on another account, or someone else has had a free trial using the same payment card that could stop you getting one. You could also try on a different browser and/or device to see if things work on there.
If that doesn't work @Tony-D from the NOW TV Team is on a bit of a roll at the moment, hopefully he might have time to help.
It won't let me get my free pass for anything it says I can have a 14 day
free trial and that won't work
@Gemma7 What happens when you try and start a free trial? As @Andy said, definitley check your payment details aswell. P.s you still get a free 14 day free trial even if you activate a voucher. Thanks