{
 "groups": [
    {
        "isPublic": true,
        "members": [
            true
        ],
        "numberOfMembers": 1,
        "groupId": "-LAOPAzMGzOd9qULPxue"
    },
    {
        "isPublic": true,
        "members": [
            true
        ],
        "numberOfMembers": 1,
        "groupId": "-LAOP7ISDI2JPzAgTYGi"
    }
 ]
}

return mFunctions
        .getHttpsCallable("addMessage")
        .call(data)
        .continueWith(new Continuation<HttpsCallableResult, String>() {
            @Override
            public String then(@NonNull Task<HttpsCallableResult> task) throws Exception {
                String result = (String) task.getResult().getData();
                return result;
            }
        });