wseixas In that case I recommend to use external monitoring - e.g. approach #2.
Create another python script, use master token to connect to flespi and subscribe it to the topic flespi/log/mqtt/sessions/+/+.
It will receive flespi/log/mqtt/sessions/XXXX/accepted and flespi/log/mqtt/sessions/XXXX/closed messages with informational payload where XXXX is client-id. You may even subscribe to exact client-id.
Try it from MQTT Board (external or embedded into flespi.io) and login/logout to flespi.io.
Do you need to help with how to send messages to Telegram?