Shelly attributes as a sensor

Hi all,
I try to create a status sensor for my Shelly devices without the need to create a separte sensor for each and single attribute that I want to fetch and to be displayed and that I can use in automations.
So far I have created a sensor similar to:

- platform: rest
  name: "Shelly1PM heatpump"
  resource: http://192.168.132.179/status
  json_attributes:
    - wifi_sta
    - temperature
    - overtemperature
  value_template: 'OK'
  scan_interval: 7200

This sensor is based on the JSON response of the /status endpoint of my Shelly device which looks like:

{
    "wifi_sta": {
        "connected": true,
        "ssid": "blablabla",
        "ip": "192.168.132.179",
        "rssi": -73
    },
    "cloud": {
        "enabled": false,
        "connected": false
    },
    "mqtt": {
        "connected": false
    },
    "time": "14:15",
    "unixtime": 1602425702,
    "serial": 42603,
    "has_update": false,
    "mac": "98F4ABB915D1",
    "cfg_changed_cnt": 36338,
    "actions_stats": {
        "skipped": 0
    },
    "relays": [
        {
            "ison": true,
            "has_timer": false,
            "timer_started": 0,
            "timer_duration": 0,
            "timer_remaining": 0,
            "overpower": false,
            "source": "http"
        }
    ],
    "meters": [
        {
            "power": 52.44,
            "overpower": 0.00,
            "is_valid": true,
            "timestamp": 1602425702,
            "counters": [
                52.646,
                52.606,
                52.722
            ],
            "total": 535267
        }
    ],
    "inputs": [
        {
            "input": 0,
            "event": "",
            "event_cnt": 0
        }
    ],
    "ext_sensors": {
        "temperature_unit": "C"
    },
    "ext_temperature": {
        "0": {
            "hwID": "2857f456b5013c8d",
            "tC": 26.50,
            "tF": 79.70
        },
        "1": {
            "hwID": "284fec56b5013c35",
            "tC": 39.19,
            "tF": 102.54
        },
        "2": {
            "hwID": "28efc456b5013caf",
            "tC": 29.62,
            "tF": 85.33
        }
    },
    "ext_humidity": {},
    "temperature": 50.13,
    "overtemperature": false,
    "tmp": {
        "tC": 50.13,
        "tF": 122.23,
        "is_valid": true
    },
    "update": {
        "status": "idle",
        "has_update": false,
        "new_version": "20200827-070450/v1.8.3@4a8bc427",
        "old_version": "20200827-070450/v1.8.3@4a8bc427"
    },
    "ram_total": 50712,
    "ram_free": 38436,
    "fs_size": 233681,
    "fs_free": 149596,
    "uptime": 616851
}

This gives me my sensor as:


But my question is:
How can I display e.g. the RSSI signal strength in my UI or use it in my automations without the need for creating a separate sensor. I tried with:

type: 'custom:multiple-entity-row'
entity: sensor.shelly1pm_heatpump
show_state: false
name: Shelly1PM
icon: 'mdi:motion'
secondary_option: last_changed
entities:
  - attribute: wifi_sta.rssi
    name: WiFi signal

But this returns nothing?
Any help is much appreciated.
Thanks

Maybe I don’t understand something but I see this:

in your image…

I am sorry that I did not myself clear. Apologize for that.
The key problem is when I try to display the attribute in lovelace. I am using the “multiple-entity-row” card

type: 'custom:multiple-entity-row'
entity: sensor.shelly1pm_heatpump
show_state: false
name: Shelly1PM
icon: 'mdi:motion'
secondary_option: last_changed
entities:
  - attribute: wifi_sta.rssi
    name: WiFi signal strength
  - attribute: temperature
    name: Device heat

But the card doesn´t recognize the value:

image

Try just:
- attribute: rssi

That´s what I tried in the very beginning. But with the same result.

- attribute: rssi

does not work. And it seems that HA does not recognize the rssi at all. When I go into an automation and want to make it dependent on the rssi attribute I only get the wifi_sta instead.