The web interface cache all channel and group names for up to 2 hours to speed up page loading. If you need to select a channel or group name, which was created in the last 2 hours, you can reload the cache by clicking on "Reload TS3 server data now" on the Bot Manager page, as seen on the following screenshot:
https://www.stefan1200.de/documentation/jts3servermod_mysql/webinterface3/reload_cache.png