element.io installer failed, because of the cert manager. Any ideas?

Question

As installing my element.io instance, the installer stopped and threw an error concerning the cert manager.

This is the error:

fatal: [localhost]: FAILED! => 
  msg: |-
    {'certmanager': {'issuer': 'letsencrypt'}} is valid under each of {'not': {'required': ['certificate', 'certmanager', 'secretName']}, 'properties': {'mode': {'pattern': 'external'}}}, {'not': {'required': ['certificate', 'secretName']}, 'properties': {'mode': {'pattern': 'certmanager'}}, 'required': ['certmanager']}
  
    Failed validating 'oneOf' in schema['properties']['global']['properties']['k8s']['properties']['ingresses']['properties']['tls']:
        {'oneOf': [{'not': {'required': ['certificate', 'secretName']},
                    'properties': {'mode': {'pattern': 'certmanager'}},
                    'required': ['certmanager']},
                   {'not': {'required': ['certmanager', 'secretName']},
                    'properties': {'mode': {'pattern': 'certfile'}},
                    'required': ['certificate']},
                   {'not': {'required': ['certificate', 'certmanager']},
                    'properties': {'mode': {'pattern': 'existing'}},
                    'required': ['secretName']},
                   {'not': {'required': ['certificate',
                                         'certmanager',
                                         'secretName']},
                    'properties': {'mode': {'pattern': 'external'}}}],
         'properties': {'certificate': {'description': 'The default '
                                                       'certificate for every '
                                                       'ingresses can be '
                                                       'configured here. It '
                                                       'can be used for '
                                                       'example if you plan to '
                                                       'use a wildcard '
                                                       'certificate, or a '
                                                       'certificate containing '
                                                       'all components fqdns '
                                                       'as SAN.',
                                        'properties': {'certFileSecretKey': {'type': 'string'},
                                                       'privateKeySecretKey': {'type': 'string'}},
                                        'type': 'object'},
                        'certmanager': {'description': 'The cert-manager '
                                                       'properties, if enabled',
                                        'properties': {'issuer': {'description': 'The '
                                                                                 'name '
                                                                                 'of '
                                                                                 'cert-manager '
                                                                                 'ClusterIssuer '
                                                                                 'to '
                                                                                 'use',
                                                                  'type': 'string'}},
                                        'type': 'object'},
                        'mode': {'description': 'The default TLS mode of '
                                                'deployed ingresses. Use '
                                                'external if TLS is managed '
                                                'externaly to the cluster, '
                                                'certmanager if you want to '
                                                'use cert manager to issue '
                                                'certificate automatically, or '
                                                'certfile if you want to '
                                                'upload certificate files to '
                                                'kubernetes tls secrets '
                                                'manually.',
                                 'enum': ['certmanager',
                                          'external',
                                          'certfile',
                                          'existing'],
                                 'type': 'string'},
                        'secretName': {'description': 'The name of a secret in '
                                                      'the cluster that '
                                                      'contains TLS '
                                                      'certificates',
                                       'maxLength': 253,
                                       'pattern': '^[a-z0-9]([\\-a-z0-9]*[a-z0-9])?(\\.[a-z0-9]([\\-a-z0-9]*[a-z0-9])?)*$',
                                       'type': 'string'}},
         'type': 'object'}
  
    On instance['global']['k8s']['ingresses']['tls']:
        {'certmanager': {'issuer': 'letsencrypt'}}

Did anyone ever experience this? I'm lost here.

I tried to install element.io via ubuntu (terminal) and the GUI (browser). The error said (as far as I can tell) sth about the cert manager and TLS errors. I tried to modify the config.yaml and deployment.yaml by adding 'issuer: letsencrypt', but it didn't help.