It is in the Options Manager...Notifications...web_cgi_url. Suggest you set it to the load balancer in front of your Application servers. Make the change while logged in to the Background Server and make sure that the parameter (NX_WEB_CGI_URL) in the NX.ENV file is updated. If not, then update yourself. Then you will have to restart the Application servers so that it propogates out to those servers.