1) did you check if UEM healthcheck as on link below?
2) If it passed did you go to monitored site and checked on network / source code if you see there agent snippet and it's running?
3) Did you see JS errors on browser console (if agent is injected). May be beacons from agent are not be able to send?
4) If your agent isn't injected, do you have monitored webServer that should inject uem (Apache / NGINX, IIS Web Server (I'm not talking about .net agent on IIS pool) / Tomcat / Jboss).
5) If agent is monitored, do you have User Experience sensor pack placed in sensor placemenent on it's AgentGroup?
6) Do you have properly Defined application in system profile? To you see assigment to created application on purepaths?
7) If application is created correctly, do you have configured UEM for this particular application with assigning proper frameworks that are used on frontend?
More throubleshooting here: