Getting error in purchase_controller.rb:37:in `credit' Line 4 here.

paypal-error

undefined method `on' for #<ActiveModel::Errors:0x007ff72d404300>

def credit
    render :action => 'index' and return unless @cc.valid?
    
    @response = paypal_gateway.purchase(price_in_cents, @cc, 
      :ip => request.remote_ip,
      :billing_address => params[:billing_address])
      
    if @response.success?
      @purchase = Purchase.create(:response => @response)
      redirect_to :action => "complete", :id => @purchase
    else
      paypal_error(@response)
    end
  end