code: def set_monthly_billing(currency, client_pays, markup_percentage,
        monthly_scheme = nil)
        options = { :body => {
          :Currency => currency,
          :ClientPays => client_pays,
          :MarkupPercentage => markup_percentage,
          :MonthlyScheme => monthly_scheme }.to_json }
        put 'setmonthlybilling', options
      end
docs: Sets the monthly billing settings for this client.
   monthly_scheme must be nil, Basic or Unlimited