The vSphere IPI documentation explains how one should configure a load balancer in place of the default load balancer. This is how the it states that the install-config should look like: [1]

===
platform:
  vsphere:
    loadBalancer:
      type: UserManaged
      apiVIPs:
      - 10.20.30.40
      ingressVIPs:
      - 10.20.30.40
===

This is incorrect and leads to an error in the installation due to an incorrect placement of the apiVIPs stanza in the install-config file.

WARNING failed to parse first occurrence of unknown field: failed to unmarshal install-config.yaml: error unmarshaling JSON: while decoding JSON: json: unknown field "apiVIPs"

According to the install-config schema [2], the paramaters apiVIPs and ingressVIPs should be outside of the loadBalancer stanza, under vsphere, like this:

===
platform:
  vsphere:
    loadBalancer:
      type: UserManaged
    apiVIPs:
    - 10.20.30.40
    ingressVIPs:
    - 10.20.30.40
===

[1] https://docs.openshift.com/container-platform/4.16/installing/installing_vsphere/ipi/installing-vsphere-installer-provisioned-network-customizations.html#nw-osp-configuring-external-load-balancer_installing-vsphere-installer-provisioned-network-customizations

[2] https://github.com/openshift/installer/blob/release-4.16/data/data/install.openshift.io_installconfigs.yaml#L4295-L4649

    All the time, if the documentation is strictly followed.

    1. Write an install-config for vsphere IPI with a user-managed load balancer, according to the documentation
    2. Run the openshift-installer using the format described in the documentation
    3. See that the installer fails to correctly pick up the apiVIPs and ingressVIPs definitions
    

WARNING failed to parse first occurrence of unknown field: failed to unmarshal install-config.yaml: error unmarshaling JSON: while decoding JSON: json: unknown field "apiVIPs"

The openshift-installer to correctly pick the apiVIPs and ingressVIPs definitions.