Unable to enable metered billing on existing subscription via API

Unable to enable metered billing on existing subscription via API

I call the following to update and existing subscription:

PUT https://subscriptions.zoho.com/api/v1/subscriptions/{id}

With body:
{
  "is_metered_billing": true
}

The response is 200 and the payload always returns with "is_metered_billing": false

The metered billing is never enabled in the portal.

How is this accomplished via the API?