From what the docs say, the mobile app is for notifications and approvals. For the switch, the web console in the phone browser works fine, that’s how I run my allotment pump.

What to set up:

1. On the Pi’s device profile, Commands tab, add a command, e.g. method heater.set, one Yes/no parameter on, tier Basic. Boards only send Basic tier commands.
2. Make a dashboard, add a Switch control, action Run a command, pick the Pi and heater.set, and bind the current state to a key the Pi reports (say heater_on as 0/1).
3. On the Pi:

def on_connect(c, u, f, rc):
    c.subscribe("v1/rpc/req/+", qos=1)

def on_message(c, u, msg):
    req_id = msg.topic.rsplit("/", 1)[1]
    body = json.loads(msg.payload)
    if body.get("method") == "heater.set":
        on = bool(body["params"]["on"])
        GPIO.output(17, on)
        c.publish("v1/telemetry", json.dumps({"heater_on": int(on)}), qos=1)
        c.publish(f"v1/rpc/res/{req_id}", json.dumps({"ok": True}), qos=1)

No ports opened. Bookmark the board on your phone’s home screen and it’s basically an app. For alerts (room too cold etc.) the app gives you push on the phone, or use e-mail or a linked chat app.