Google Actions Builder stops execution when selecting a visual item from a List

Question

I'm pulling my hairs here. I have a Google Assistant application that I build with Jovo 4 and Google Actions Builder.

The goal is to create a HelpScene, which shows some options that explain the possibilities/features of the app on selection. This is the response I return from my Webhook. (This is Jovo code, but doesn't matter as this returns a JSON when the Assistant calls the webhook.)

@Handle(GoogleAssistantHandles.onScene('HelpScene'))
  showHelpList() {
    return this.$send({
      platforms: {
        googleAssistant: {
          nativeResponse: {
            scene: {
              name: this.jovo.$googleAssistant?.$request.scene?.name,
              slots: {},
              next: {
                name: 'MainScene',
              },
            },
            session: {
              id: 'session_id',
              languageCode: 'nl-BE',
              params: {},
              typeOverrides: [
                {
                  name: 'prompt_option',
                  synonym: {
                    entries: [
                      {
                        name: 'ITEM_1',
                        synonyms: ['Item 1', 'First item'],
                        display: {
                          title: 'Item #1',
                          description: 'Description of Item #1',
                          image: {
                            alt: 'Google Assistant logo',
                            height: 0,
                            url: 'https://developers.google.com/assistant/assistant_96.png',
                            width: 0,
                          },
                        },
                      },
                      {
                        name: 'ITEM_2',
                        synonyms: ['Item 2', 'Second item'],
                        display: {
                          title: 'Item #2',
                          description: 'Description of Item #2',
                          image: {
                            alt: 'Google Assistant logo',
                            height: 0,
                            url: 'https://developers.google.com/assistant/assistant_96.png',
                            width: 0,
                          },
                        },
                      },
                      {
                        name: 'ITEM_3',
                        synonyms: ['Item 3', 'Third item'],
                        display: {
                          title: 'Item #3',
                          description: 'Description of Item #3',
                          image: {
                            alt: 'Google Assistant logo',
                            height: 0,
                            url: 'https://developers.google.com/assistant/assistant_96.png',
                            width: 0,
                          },
                        },
                      },
                      {
                        name: 'ITEM_4',
                        synonyms: ['Item 4', 'Fourth item'],
                        display: {
                          title: 'Item #4',
                          description: 'Description of Item #4',
                          image: {
                            alt: 'Google Assistant logo',
                            height: 0,
                            url: 'https://developers.google.com/assistant/assistant_96.png',
                            width: 0,
                          },
                        },
                      },
                    ],
                  },
                  typeOverrideMode: 'TYPE_REPLACE',
                },
              ],
            },
            prompt: {
              override: false,
              content: {
                collection: {
                  items: [
                    {
                      key: 'ITEM_1',
                    },
                    {
                      key: 'ITEM_2',
                    },
                    {
                      key: 'ITEM_3',
                    },
                    {
                      key: 'ITEM_4',
                    },
                  ],
                  subtitle: 'List subtitle',
                  title: 'List title',
                },
              },
              firstSimple: {
                speech: 'This is a list.',
                text: 'This is a list.',
              },
            },
          },
        },
      },
    });

I created a HelpScene which pulls my options from my webhook.

In my slot filling, this is the configuration.

When I use the simulator, the options from my webhook are shown perfectly. But when I click an item in the list, the app just stops working. "YourApp is currently not responding".

At first I thought it had something to do with my webhook, so I changed the behaviour of the "on slot is filled" condition, that it should prompt something, directly from Google Actions Builder, but the behaviour is still not desired: the app just stops working.

Any ideas what I'm doing wrong?

Thanks in advance!