JSON MQTT payload access in automation

Configuration
,
1

I set up a simple automation that listens to an MQTT topic and sends the messages ({{ trigger.payload }}) to my phone.

It works well, except I get the following error if the message is a serialised JSON object:
template value should be a string for dictionary @ data['message']

Is there some way to cast trigger.payload to a string, or to disable whatever is parsing the object in the first place? I tried {{ trigger.payload | string }}, but it didn’t help.

For now I’ve switched to serialising the messages as YAML.

This topic seems vaguely similar: Automation trigger on MQTT message with JSON payload not triggering - #2 by 123

Automation YAML:

alias: My alert
description: ""
trigger:
  - platform: mqtt
    topic: mytopic
condition: []
action:
  - device_id: deadbeef
    domain: mobile_app
    type: notify
    message: "{{ trigger.payload }}"
    title: Update
mode: single
2

Maybe this:

https://www.home-assistant.io/docs/configuration/templating/#tofrom-json

action:
  - device_id: deadbeef
    domain: mobile_app
    type: notify
    message: "{{ trigger.payload | from_json }}"
    title: Update
3

Thank you! to_json is what I needed. The output ends up being enclosed in quotes, and quotes in the serialised string are escaped ("{\"MyKey\": \"MyValue\"}"), but at least it works.