I am assuming you are using a NowTV stick with a bundled 3 months pass ?
How far have you got in the setup of the stick ?
If your stick is fully setup and you have gone to My Account > Passes & Vouchers whilst logged in here and you have redeemed the voucher on your account.
Where the error message is happening when attempting to watch anything with your pass which is active, then i would try either a full factory reset on your Router or maybe switch the power off on your Router for about 30 minutes.
Also if you are using a VPN on your Router then disable it, where it sounds to me the error may be possibly geographically related or possibly a rouge IP address on your Router.