order_controller_callbacks.rb

module Extensions
  module Spree
    module CheckoutCallbacks
      extend ActiveSupport::Concern

      included do
        set_callback :updating_from_params, :after, :clear_empty_payment

        def clear_empty_payment
          #self in this case is the order object
          byebug
          if self.payments && self.payments.count > 1
            self.payments.last.delete
          end
        end
      end
    end
  end
end
::Spree::Order::Checkout.send(:include, Extensions::Spree::CheckoutCallbacks)