I giorni non possono essere selezionati

In case the days in your calendars are all empty, it probably means that you missed to configure something from the back-end.

If your calendars look like the image below and nothing happens when you click the days, you probably forgot to assign your services to your employees (at least one).

Services must be assigned at least to one employee in order to make them available, as the availability is completely based on the working days of the employees. Otherwise, all the days will be considered as unavailable.