With a mobile sports pass you can only use it on a smartphone (nothing else).
Plus you are restricted to only five channels which are Sky Premier League, NFL (Action), Arena, Racing (Horses) and News.
See if the mobile pass plays on a smartphone when trying Sky Sports Premier League for example using the NowTV App on your smartphone and not using an internet browser.
If no joy, try deleting the NowTV App and download a fresh NowTV App from your smartphone Apps Store.
Just remember if you don't want to continue to use the mobile pass after the Nike voucher is up, that you cancel the pass fully to stop the pass auto renewing each month.
With a month pass i tend to cancel them a couple of days before the voucher is about to finish on my account.
Anyway glad you got the mobile pass running 👍.