Hi @Anonymous User
Are you using the NowTV App from your phones App store and not using an internet browser on the NowTV website ?
When using the NowTV App on the phone are you trying to watch Sky Sports Premier league, Sky Sports Action, Sky Sports Arena, Sky Sports Racing or Sky Sports News which are the only five channels available to watch with a NowTV Sports Mobile Pass.
If still no luck, then delete the NowTV App and re install again and re sign back into the App on your phone.
When you sign back in, make sure it's the same log in details when you go to My Account > Passes & Vouchers on here where hopefully it shows you mobile sports pass is active.
