Hi,
Just a heads up that the DUO api url you posted if visited generates the error listing your vault URL so you may want to edit your post and remove the link?
The error is from DUO stating that the redirect link must be https, so more likely to be a DUO policy update than a bitwarden one if you haven’t changed any settings.
Having said that, is the url set in your config.yml set to http or https? Bitwarden will redirect to https, but if the url in the config is set to http that will proably be sent to DUO as the return link and that may be causing the error.
e.g. /opt/bitwarden/bwdata/config.yml
#Full URL for accessing the installation from a browser. (Required)
url: https://xxxxxxxxxxxx
If you update the config, don’t forget to run
./bitwarden.sh rebuild
from the /opt/bitwarden directory afterwards