On fresh OctoPi installation npm install fails

[ScruffR]

When I run sudo npm -g i marlin-conf I always get this error

...
npm ERR! command git --no-replace-objects ls-remote ssh://git@github.com/MelvinTo/node-nat-upnp.git
npm ERR! git@github.com: Permission denied (publickey).
...

Although when I check ssh -T git@github.com I'm successfully authenticated.

On the other hand running the install without sudo fails due to lacking permissions to create /usr/lib/node_modules/marlin-conf

---

System info

RPi 3B+
Raspbian GNU/Linux 10 (buster)
raspbian
OctoPrint: 1.7.3
OctoPi   : 0.18.0
node     : v17.4.0
npm      : 8.3.1