What I have noticed is that the public WAN IP shown on my asus is different to the one that 'can you see me' populates. Could this be why?
Likely you are on CGNAT for IPv4 which is because the IPv4 addresses have run out and new ISP such as Hey! cannot purchase any. So there is a 'router' in the ISP network that shares the public IP with lots of customers. Some ISPs provide IPv6 at the same time with plenty of addresses, other ISPs will sell you a public routable IP for extra money.
Talk to the ISP and ask about CGNAT and what it stops you doing.
Thinkbroadband's main site has a page that shows you the IP address you are coming from, when it is not the same as the one on your own router, CGNAT is likely. (and the IP on your router could be 10.x.x.x perhaps?)
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