"It should detect DHCPv6 if set to Auto-detect" - it doesn't.
"Should also ask, what size prefix delegation are you requesting?" - I'm not "requesting" anything. Whatever they send, probably a /64
Can I please get an actual answer, not vague guesses? There are settings in there. I do not know what they should be. Can someone just tell me what settings have to be applied to make this work on Cox?
Going to need more data from your side on what exactly those different settings are. Can you upload a screenshot? Also, you could be a tad nicer. All we can do is guess since none of us have your exact modem/gateway.