Can't verify CSRF token authenticity in rails

I am using PaypalAdaptive. It sends ipn_notification properly. ipnNotification action method is as following -

def ipn_notification
    ipn = PaypalAdaptive::IpnNotification.new
    ipn.send_back(request.raw_post.to_json)

    print "=====================request.raw_post#{request.raw_post}=============="

    if ipn.verified?
        PaymentMailer.notify_unknown(request.raw_post).deliver
    else
        logger.info "IT DIDNT WORK"
    end
    render :nothing => true
end

but it's returning error

WARNING: Can't verify CSRF token authenticity rails

Any help for this problem.