I've got the same offer and the same error code when I click on the link. Very frustrating and impossible to actually contact anyone at NOWTV. The code expires this week so keen to get an answer soon...
Hi @Anonymous User
When you open my previous link there should be a chat button to click on in green.
If no luck try a different internet browser with live chat.
I believe the live chat opening hours is reduced because of Covid-19 between 8am to 8pm.
If you can't get through try after 8am tomorrow.