I can not use checkboxes in vuejs

Hello, I have tried the way in which the documentation of vue indicates and works with a variable not yet assigned to the time that I assign,

                           <div class="form-check">
                                <label class="form-check-label">
                                <input type="checkbox" class="form-check- 
                                input" value="lunes"
                                v-model="usuario.condiciones">
                                Lunes
                                </label>
                            </div>
                            <div class="form-check">
                                <label class="form-check-label">
                                <input type="checkbox" class="form-check- 
                               input" value="martes"
                                v-model="usuario.condiciones">
                                Martes
                                </label>
                            </div>
                             <br>
                                 <p><strong>Dias: </strong> 
                                 {{usuario.condiciones}}</p>

                            <script>
                 data (){
                        return {
                      usuario: {

                      condiciones: []
                  },

This picks up the fix.

when the user object is changed by a variable already assigned and running in a field of the DB. It stops working I do not know what to do anymore.

Another is to assign directly without converting into a collection of objects, but the only thing that checkboxes do is at the same time fill up and only give Boolean values.

Thanks and regards to all