Are you on a current sports pass offer with more than 30 days remaining ?
Or have you an active one day or one week sports pass currently running or saved on your account ?
Are your bank card details on your account up to date ?
Are you a BT TV customer who subscribe directly to BT for your NowTV Passes ?
Have you tried a different internet browser when attempting to take up the offer ?
When attempting to take the offer, if the same offer is not under My Account > Manage Account > My Passes to take up, then see if by going through the website offer process that a NowTV voucher code is embedded at the end of the URL address bar usually starts with NOW or SPM and if so try manually applying the code directly on your account.
Otherwise see if live chat can assist (use the link below).