Having an issue with remote access after new ISP

My remote access was working perfectly before, was using a cable internet connection. About a month ago, i switches providers who was installing FTTH. Since then, my remote access hasn’t been working for my plex server.
Using my ISP’s fiber modem thing, and my own router, which i’ve been using for a few years now, ASUS N66U.

On my plex remote access page, I’m receiving:
“Not available outside your network
Your server is signed in to Plex, but is not reachable from outside your network. Learn more
Tip: It looks like your server may be connected to the internet through multiple routers or other network devices. Try connecting it directly to your primary device, or visit our support site for more information about troubleshooting this “Double-NAT” scenario.”

I contacted my ISP and they said they use a nat connection, and many customers use port forwarding for gaming and such.
I’ve since set up a static IP connection on my MacBook Pro, logged into my router, set up port forwarding using that ip address and port 32400. (not sure if i’ve set everything up correctly, but my N66U says its receiving a static ip from this MacBook, so i think that part is correct)
But when I click on the canyouseeme link and check port 32400, it says “Error: I could not see your service on port (32400)
Reason: Connection refused”

And my plex server says this still.

Can someone please assist?