Trying to add Yubikey, gives network error

I’ve been selfhosting Bitwarden on an Ubuntu server for some time. Untill now, I’ve used Authy for 2FA.
I’ve recently bought 2 Yubikey 5 NFC’s and I’m trying to use these instead of Authy. However, when I try to add the first key I get an error: ‘an unhandled server error has occurred’.

  • I’ve completed the Yubico API key signup and added the details to global.override.env
  • I’ve checked that app-id.json is present.

Ubuntu server is 22.04
Bitwarden is version 2023.2.0.

I’m an amateur so I’m struggling to find a solution. I am accessing the server on port 8089 (https// Would that make any difference? I noticed that the app-id.json file states:

0	""
1	"ios:bundle-id:com.8bit.bitwarden"
2	"android:apk-key-hash:dUGFzUzf3lmHSLBDBIv+WaFyZMI"

It doesn’t use the port number in the URL. Would that be a possible issue?
Is there anything I can do to further diagnose/solve this issue?