First, check to see if Webex Teams is up and running properly. You can check https://status.webex.com to get the latest status. Or, on Webex Teams for Windows and Mac, you can also use the Health Checker within the app itself.
You should also make sure you don't have anything on your Wi-Fi network, such as a firewall, that might be preventing you from using Webex Teams. If you are using Webex Teams for iPhone, iPad, or Android, try switching to your mobile data connection. If the app works when you're connected to mobile data, then the Wi-Fi connection might be blocking Webex Teams traffic. If you're using Webex Teams at work, report this issue to your administrator.
If the problems persist, you can contact your company's support team, or open a support case for Webex Teams.