code: func (r Billing_Invoice_Item) GetTotalOneTimeAmount() (resp datatypes.Float64, err error) {
  	err = r.Session.DoRequest("SoftLayer_Billing_Invoice_Item", "getTotalOneTimeAmount", nil, &r.Options, &resp)
  	return
  }
docs: // Retrieve An invoice Item's total, including any child invoice items if they exist.