Problems moving from a Raspberry Pi to a MT2500A (Brume 2)

I have had to move from a static IP to using a DDNS service (no-ip), so as PiVPN has died, and the Raspberry Pi became a hassle, I decided I should go down a better road for my Wireguard server and bought a Brume 2.
As the Rpi, using PiVPN “just worked”, I thought that the Brume 2 would too.
It doesn’t - I’m having huge problems, and I just can’t link up to it via a different network,
I use Windows 11, ASUS ZenWifi AX mesh system and Bitdefender plus Malwarebytes premium for defence.
Nothing has changed since I was successful previously with my static IP and Rpi.
I’m a bit of a novice…
Help (I don’t want to return the Brume 2)!