Zapier Custom Action doesn't pass through data from a dynamic field select list

For an action I use a dynamic field containing a list of users (ids / labels). I collect the users via Rest API and they are presented in the UI.

I defined the list in the dynamic field code like:

    const options = {
        url: 'https://<mysite>.ngrok.io/rest/1.0/<my endpoint>?expand=users',
        method: 'GET',
        headers: {
            'Accept': 'application/json',
            'Authorization': `Bearer ${bundle.authData.api_key}`
        }
    }

    return z.request(options)
        .then((response) => {
            response.throwForStatus();
    
        return {
          key: 'coverers',
          label: 'Coverers for automatic reassigns',
          placeholder: 'Choose a coverer',
          choices: response.json.users,
          list: true
        }
    });

In the API request for the action I define the "coverers" property and it is filled with an array of the size of the number of users I add in the UI. But the values are all empty objects [{}, {}, {}]. The code for this is:

       const options = {
        url: 'https://<my site>.ngrok.io/rest/1.0/<my endpoint>',
        method: 'POST',
        headers: {
            'Content-Type': 'application/json',
            'Accept': 'application/json',
            'Autorization': `Bearer ${bundle.authData.api_key}`
        },
        params: {
    
        },
        body: {
            'startDate': bundle.inputData.startDate,
            'endDate': bundle.inputData.endDate,
            'coverers': bundle.inputData.coverers,
            'message': bundle.inputData.message
        }
    }
    
    return z.request(options)
        .then((response) => {
        response.throwForStatus();
        const results = response.json;
    
        // You can do any parsing you need for results here before returning them
    
        return results;
    });

The rest api endpoint for the dynamic field returns:

    [{
        "value": "xxxxx0c1c5e69a1",
        "sample": "xxxxx0c1c5e69a1",
        "label": "Ad Mihn"
    },
    {
        "value": "xxxxx0da21fdb29",
        "sample": "xxxxx0da21fdb29",
        "label": "Barbi Queue"
    },
    {
        "value": "xxxxx0da389dbb1",
        "sample": "xxxxx0da389dbb1",
        "label": "Mark Ating"
    }]

Obviously the selected users are not correctly translated, but what am I missing? How can I get the selected user information? 

  [1]: https://i.stack.imgur.com/tTNQM.png