Hi @Anonymous User
Was that email offer for 1 month nowtv sports pass for £20 with a free Sky Sports Box Office code to watch the Joshua fight ?
If so, then the way it worked on the previous Joshua fight is that you will receive a code by email and instructions on the day of the fight.
If it's a different email offer, then maybe provide some more info about it here.
Here's a help guide, where the last help topic mentions about the nowtv fight bundled deal.