Comment 13 for bug 1939389

In the above mentioned template, there is a "project_domain_name" and "user_domain_name" set if "admin_domain_name" is set. With the project_domain_name set, the keystone client used by the nova client should have the proper context.

I would suggest you do a:

charm pull cinder

add the template mentioned above, then do an upgrade of the charm using the locally modified version.

After hooks run, you should have the proper nova section with the needed settings, and the error should no longer manifest, as the nova client will have proper credentials.