Ansible Fortigate vip configuration with ssl certificate

Question

I am trying to configure my Fortigate 60E using the Ansible FortiOS Galaxy plugins. Currently I am working on the vip configuration. For most of the vips it is working fine but I can't get the ssl vip to work.

I would like to set up a ssl vip of type server-load-balancer like this:

- name: "Configure {{ vdom }} vdom virtual IP for IPv4"
  fortios_firewall_vip:
    vdom:  "{{ vdom }}"
    state: "{{ state }}"
    access_token: "{{ token }}"
    firewall_vip:
      name: "vip_ssl_placeholder"
      extintf: "management"
      extip: "10.10.10.1"
      extport: "6363"
      type: "server-load-balance"
      server_type: "ssl"
      monitor:
      - name: "tcp-6363-link-monitor"
      ldb_method: "least-rtt"
      persistence: "ssl-session-id"
      realservers:
      - id: "1"
        ip: "10.16.10.1"
        port: "6363"
      - id: "2"
        ip: "10.16.10.2"
        port: "6363"
      ssl_mode: "full"
      ssl_certificate: "Fortinet_Factory"

However, when applying the script I get an error -56 from the Fortigate, telling me there there should be at least 1 server certificate. The certificate is yet installed. Here is the Ansible output showing the error:

meta:
    build: 2571
    cli_error: |-
      current vf=root:0
      There must be at least 1 server certificate configured.
      attribute set operator error, -56, discard the setting
      Command fail. Return code -56
    error: -56
    http_method: POST
    http_status: 500
    name: vip
    path: firewall
    revision: 18eaa14db7184d138cc857f49e1819a3
    revision_changed: false
    serial: FGT60Exxxxxxxxx
    status: error
    vdom: root
    version: v7.4.2
  msg: Error in repo

I am using Ansible [core 2.14.12], Ansible-Galaxy plugin fortinet.fortios 2.3.4 and a Fortigate 60E with FortiOS7.4.2

I have tried to setup the vip manually using the Fortigate GUI, this works and I can also select the certificate mentioned above.

I have also checked the commandes used by the manual setup on the Fortigate CLI itself with

diag deb en
diag deb cli 8

and the commands issued by the system are the same.

What is it that I am missing? What does the Fortigate error mean?