Parsing argument error in buttons

I need some help please , the buttons used to work but suddenly i got this error despite i didn’t made any changes … Any suggestions please ??

Hi! :smiley: What rasa version are you using?

Can you make a little test just using just one {} ?

{"title": "happy" , "payload": '/happy{"slot_name":"just a test"}'}

my actions.py

from typing import Any, Text, Dict, List

from rasa_sdk import Action, Tracker
from rasa_sdk.executor import CollectingDispatcher

class ActionHelloWorld(Action):
    def name(self) -> Text:
        return "action_hello_world"
    def run(self, dispatcher: CollectingDispatcher,
            tracker: Tracker,
            domain: Dict[Text, Any]) -> List[Dict[Text, Any]]:
            
        buttons = []

        #append the response of API in the form of title and payload

        buttons.append({"title": "happy" , "payload": '/happy{"slot_name":"just a test"}'})

        #then display it using dispatcher

        dispatcher.utter_message(text="message you want to display" , buttons=buttons)
        return []

my domain.yml

version: "3.0"

entities:
- slot_name

intents:
  - greet
  - happy

actions:
  - action_hello_world

slots:
  slot_name:
    type: text
    mappings:
    - type: from_entity
      entity: slot_name

 
  
responses:

  utter_happy:
  - text: "Great, carry on! {slot_name}"

session_config:
  session_expiration_time: 60
  carry_over_slots_to_new_session: true

  

It works now thank you