curl --request GET \
  --url https://api.example.com/api/v1/workspaces/{workspace_id}/billing/change-plan/preview \
  --header 'X-API-Key: <api-key>'

{
  "currency": "<string>",
  "next_invoice_amount": 123,
  "next_invoice_date": "2023-11-07T05:31:56Z",
  "next_invoice_proration": 123,
  "next_invoice_recurring": 123,
  "promotion_code_applied": "<string>",
  "prorated_today": 123,
  "target_plan": "<string>",
  "warnings": [
    {
      "current_count": 123,
      "new_limit": 123,
      "overflow": 123
    }
  ],
  "coupon_applies_to_target": true,
  "coupon_id": "<string>",
  "coupon_name": "<string>"
}