Not connected status for mqtt server in ignition gateway

A new mqtt server created in ignition gateway → Settings → Mqtt engine → Server.
The server address provided in the format tcp://:8883. But the server shows not connected.
Mosquitto broker is running on the same system. And the ignition is in trial mode.
Please suggest on the query.
Attached is the screenshot of ignition gateway.
Let us know if any further details requied.