It can have two reasons, why the Web Interface shows the bot status "bot unknown".
First:
You didn't follow the installation order while the installation of the JTS3ServerMod and the Web Interface. If the JTS3ServerMod Query Interface was not setup correctly while you created the bot with the Web Interface, the JTS3ServerMod just didn't know that this bot exist. Use the instance list reload command on the bot list page in the Web Interface or just restart the JTS3ServerMod process, if this is the reason.
Second:
The JTS3ServerMod and the Web Interface don't use the same MySQL database. In this case the JTS3ServerMod can't know anything about this bot, because that bot does not exists in the own database. Make sure, that the Web Interface and the JTS3ServerMod really use the same MySQL database on the same server!