[solved] Moving Nextbox, new IP -> unreachable?

I certainly should have asked here before, but I just moved my NextBox from one location to another, and I find myself unable to reach it even locally (neither on nextbox.local nor on its LAN IP, I only can ping it successfully).
My NB setup involves dynamic DNS via deSEC / dedyn.io, but I am no specialist at all. By loging in deSec, I see things that I interpret as records that point to my former address (is that right?) and I imagine these were created directly by the NextBox initially, but how can I correct them?
(and is this the thing to do to begin with??)

I managed to ssh in the machine through the nextbox.local IP, and since then, I do manage to reach the server on the LAN with nextbox.local -but the dedyn.io way still fails.

Having reached this interface I then deactivated and reactivated the backward proxy way (via nextbox.link) and this too works now… in spite of repeated failure warnings!
(" Your NextBox Quickstart Remote Access is active, you can access your Nextcloud instance using …", but, just below, “Failed connecting through backwards-proxy, please restart the proxy configuration by disabling and enabling it.”)

… but dedyn still fails; it seems I cannot trigger its activation again :frowning:

[last edit] that was due to the router here (a french Bouygues ‘box’) in which I had to descend quite deeply to route incoming connections to the NextBox…

TIA for any advice!