@anaye 

A previous user used the bridge option when setting up here with the AX1500 and IPv6: https://community.tp-link.com/us/home/forum/topic/255340

@Tony 

I saw the other posting and I tried setting it to the Pass Through Bridge but that didn't seem to change anything.

Are there any other settings I may need to change?

And how do I know that it is actually working?

Other than going to...

www.test-ipv6.com

I tried calling Wave Broadband but trying to get someone that knows more than I do (which isn't much) is impossible.

I found this on their website...

    Ensure the "WAN connection type" is set to SLAAC

    Ensure the "IPv6 Address Assign Type" is set to SLAAC in the "LAN Setup" area

But these instructions where for an Archer C7 which is what I am replacing and that didn't work.