Hi @Anonymous User
Double check your payment details are up to date.
Have you tried a different internet browser or another device when attempting to get this offer ?
I tend to use MS Edge when on the NowTV website, also NowTV over on Twitter tends to recommend Fire Fox if customers are having problems on their website.
If that doesn't work see it when clicking on the offer, under the URL Address bar there is an embedded voucher code normally starts with NOW************** with a combination of capital letters and numbers approx 12 or 14 digits long.
Should there be a code, copy it and manually apply the code next to the relevant pass.
Don't know what the offer deal is like, but sometimes NowTV Gift Card vouchers work out similar or cheaper.