Hi @Anonymous User
See if using a different internet browser or another device with a browser on it makes any difference.
Or see if using your internet browser in a Private Window or Incognito mode gets you past the error message.
It using a VPN, then try disabling it when attempting to take the offer
Other than that, take a screen shot of the retention offer and pop over to NowTV live chat.
Use the green chat online button on this link page below.
https://help.nowtv.com/article/how-to-submit-a-complaint