Running the following command:

$ juju run --unit postgresql/0 "charms.reactive -p set_flag postgresql.cluster.initial-check"

moves the charm forward, however, it fails with the following errors:

2019-06-06 08:13:35 DEBUG update-status Authorization Failure. Authorization Failed: (http://172.18.0.109:35357/v3/tokens): The resource could not be found. (HTTP 404) (Request-ID: req-b6f8785c-890a-400b-a8cc-568a96cad6f1)
2019-06-06 08:13:35 ERROR juju-log Hook error:
Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-postgresql-1/.venv/lib/python3.6/site-packages/charms/reactive/__init__.py", line 73, in main
    bus.dispatch(restricted=restricted_mode)
  File "/var/lib/juju/agents/unit-postgresql-1/.venv/lib/python3.6/site-packages/charms/reactive/bus.py", line 390, in dispatch
    _invoke(other_handlers)
  File "/var/lib/juju/agents/unit-postgresql-1/.venv/lib/python3.6/site-packages/charms/reactive/bus.py", line 359, in _invoke
    handler.invoke()
  File "/var/lib/juju/agents/unit-postgresql-1/.venv/lib/python3.6/site-packages/charms/reactive/bus.py", line 181, in invoke
    self._action(*args)
  File "/var/lib/juju/agents/unit-postgresql-1/charm/reactive/postgresql/wal_e.py", line 154, in ensure_swift_container
    subprocess.check_call(cmd, universal_newlines=True)
  File "/usr/lib/python3.6/subprocess.py", line 291, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['/snap/bin/wal-e.envdir', '/etc/postgresql/10/main/wal-e.env', '/snap/bin/wal-e.swift', 'post', 'backup']' returned non-zero exit status 1.

2019-06-06 08:13:35 DEBUG update-status /var/lib/juju/agents/unit-postgresql-1/charm/reactive/postgresql/helpers.py:107: YAMLLoadWarning: calling yaml.load() without Loader=... is deprecated, as the default Loader is unsafe. Please read https://msg.pyyaml.org/load for full details.
2019-06-06 08:13:35 DEBUG update-status   return yaml.load(f)
2019-06-06 08:13:35 DEBUG update-status Traceback (most recent call last):
2019-06-06 08:13:35 DEBUG update-status   File "/var/lib/juju/agents/unit-postgresql-1/charm/hooks/update-status", line 22, in <module>
2019-06-06 08:13:35 DEBUG update-status     main()
2019-06-06 08:13:35 DEBUG update-status   File "/var/lib/juju/agents/unit-postgresql-1/.venv/lib/python3.6/site-packages/charms/reactive/__init__.py", line 73, in main
2019-06-06 08:13:35 DEBUG update-status     bus.dispatch(restricted=restricted_mode)
2019-06-06 08:13:35 DEBUG update-status   File "/var/lib/juju/agents/unit-postgresql-1/.venv/lib/python3.6/site-packages/charms/reactive/bus.py", line 390, in dispatch
2019-06-06 08:13:35 DEBUG update-status     _invoke(other_handlers)
2019-06-06 08:13:35 DEBUG update-status   File "/var/lib/juju/agents/unit-postgresql-1/.venv/lib/python3.6/site-packages/charms/reactive/bus.py", line 359, in _invoke
2019-06-06 08:13:35 DEBUG update-status     handler.invoke()
2019-06-06 08:13:35 DEBUG update-status   File "/var/lib/juju/agents/unit-postgresql-1/.venv/lib/python3.6/site-packages/charms/reactive/bus.py", line 181, in invoke
2019-06-06 08:13:35 DEBUG update-status     self._action(*args)
2019-06-06 08:13:35 DEBUG update-status   File "/var/lib/juju/agents/unit-postgresql-1/charm/reactive/postgresql/wal_e.py", line 154, in ensure_swift_container
2019-06-06 08:13:35 DEBUG update-status     subprocess.check_call(cmd, universal_newlines=True)
2019-06-06 08:13:35 DEBUG update-status   File "/usr/lib/python3.6/subprocess.py", line 291, in check_call
2019-06-06 08:13:35 DEBUG update-status     raise CalledProcessError(retcode, cmd)
2019-06-06 08:13:35 DEBUG update-status subprocess.CalledProcessError: Command '['/snap/bin/wal-e.envdir', '/etc/postgresql/10/main/wal-e.env', '/snap/bin/wal-e.swift', 'post', 'backup']' returned non-zero exit status 1.
2019-06-06 08:13:35 ERROR juju.worker.uniter.operation runhook.go:132 hook "update-status" failed: exit status 1

which is most likely a different issue.