The fact that the device is online means that it successfully connected to the broker. The fact that it does not operate implies that it does not receive commands or that the payload of the command is not the right one.
If you do not see its state then the tele topic is wrong.
Are you sure that the switch receives the right command, or receives any command at all? What does the console on the tasmota show?
Is the tele topic on the console equal to what you have in your configuration? Are you able to operate the switch with mosquitto_pub command?