Amend failover IP address for existing VPG via API

Hello

I am having trouble with NIC configuration via the API using a powershell script > REST call. I already have automation to create VPGs. I wish to be able to add failover IP address config to a given VM (values currently unset). I have spent a long time trying to get this to work (following the most recent API documentation) to no avail. I can save the changes I require to the vpgsettings object, but get a 500 error on commit.

I can successfully:

(1) Establish connection with ZVM / talk with APIs (v 8.5).

(2) Get GUID identifiers of VM/VPG/VPGSettingsObject.

(3) Call https://server:9669/v1/vgpSettings/<vpgSettingsIdentifier>/vms/<vmIdentifier>/nics/<nicIdentifier with the JSON body appropriately formatted as per the April  2021 documentation.

(4) I can verify that I have managed to save the changes to the vpgsettings object (by comparing it before/after a PUT call to save the vpgsettings object)

The settings object looks good, the PUT has worked, but I get a useless 500 error on POST to commit. The API clearly doesn’t like something but no hint about what that might be. Please can someone post a working example of some PowerShell / JSON that would update Failover network IP config for a VM in an existing VPG so I can compare?

Thanks, Derek