SetSlot in custom action not working

Hi. I am trying to set a slot via a custom action based on a recognized emotional state. the custom action works, but the SetSlot does somehow not. Has anyone a hint?

Custom Action:

from typing import Any, Text, Dict, List

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

from transformers import pipeline
classifier = pipeline("text-classification", model="j-hartmann/emotion-english-distilroberta-base", return_all_scores=True)

class ActionEmotion(Action):

    def name(self) -> Text:
        return "action_emotion"

    def run(self, dispatcher: CollectingDispatcher,
            tracker: Tracker,
            domain: Dict[Text, Any]) -> List[Dict[Text, Any]]:

        text = str(tracker.latest_message["text"])

        emotion = classifier(text)
        output = emotion[0]
        keys = []
        values = []
        for i in output:
            for j in i.values():
                if type(j) == str:

        newdict = dict(zip(keys, values))
        max_key = max(newdict, key=newdict.get)

        dispatcher.utter_message(text="top emotion is: {}".format(max_key))

        return [SlotSet("emotion", max_key)]


    type: categorical
      - anger
      - disgust
      - fear
      - joy
      - neutral
      - sadness
      - surprise
      - type: custom
        action: action_emotion

Output from rasa --debug:

2022-10-22 15:19:59 DEBUG rasa.core.processor - Action ‘action_emotion’ ended with events ‘[BotUttered(‘top emotion is: fear’, {“elements”: null, “quick_replies”: null, “buttons”: null, “attachment”: null, “image”: null, “custom”: null}, {}, 1666444799.731138)]’. 2022-10-22 15:19:59 DEBUG rasa.core.processor - Current slot values: firstname: None emotion: None audience: None sex: None session_started_metadata: None