Config-changed hook failed when relation to Indico charm

After deploying the content cache charm with Indico charm and the nginx-ingress-integrator the config-changed hook fails.

The content cache charm is configured as follows:
juju config content-cache-k8s backend='https://test.indico/'
juju config content-cache-k8s site='test.indico'

and trace is the following:

Traceback (most recent call last):
  File "./src/charm.py", line 278, in <module>
    main(ContentCacheCharm, use_juju_for_storage=True)
  File "/var/lib/juju/agents/unit-content-cache-k8s-0/charm/venv/ops/main.py", line 406, in main
    _emit_charm_event(charm, dispatcher.event_name)
  File "/var/lib/juju/agents/unit-content-cache-k8s-0/charm/venv/ops/main.py", line 140, in _emit_charm_event
    event_to_emit.emit(*args, **kwargs)
  File "/var/lib/juju/agents/unit-content-cache-k8s-0/charm/venv/ops/framework.py", line 278, in emit
    framework._emit(event)
  File "/var/lib/juju/agents/unit-content-cache-k8s-0/charm/venv/ops/framework.py", line 722, in _emit
    self._reemit(event_path)
  File "/var/lib/juju/agents/unit-content-cache-k8s-0/charm/venv/ops/framework.py", line 767, in _reemit
    custom_handler(event)
  File "./src/charm.py", line 67, in _on_config_changed
    self.configure_workload_container(event)
  File "./src/charm.py", line 134, in configure_workload_container
    container.start(CONTAINER_NAME)
  File "/var/lib/juju/agents/unit-content-cache-k8s-0/charm/venv/ops/model.py", line 1046, in start
    self._pebble.start_services(service_names)
  File "/var/lib/juju/agents/unit-content-cache-k8s-0/charm/venv/ops/pebble.py", line 802, in start_services
    return self._services_action('start', services, timeout, delay)
  File "/var/lib/juju/agents/unit-content-cache-k8s-0/charm/venv/ops/pebble.py", line 831, in _services_action
    raise ChangeError(change.err, change)
ops.pebble.ChangeError: cannot perform the following tasks:
- Start service "content-cache" (cannot start service: exited quickly with code 1)

Reproduction steps:
juju deploy postgresql-k8s
juju deploy redis-k8s redis-cache
juju deploy redis-k8s redis-broker
juju deploy nginx-ingress-integrator
juju trust nginx-ingress-integrator --scope=cluster
juju deploy indico --config site_url=https://test.indico

juju relate redis-cache indico
juju relate redis-broker indico
juju relate indico postgresql-k8s:db
juju relate indico:ingress nginx-ingress-integrator:ingress

juju deploy content-cache-k8s --channel edge --series groovy --force
juju config content-cache-k8s backend='https://test.indico/'
juju config content-cache-k8s site='test.indico'
juju relate nginx-ingress-integrator content-cache-k8s:ingress