Since we can not do an live availability request to your site, it is important to send us always up to date availabilities, otherwise the customer will be redirected to your page and will not be able to book there, which will result in a bad user experience and therefore in a bad performance. Initially all days are considered "unknown" and will be shown as unavailable on our site unless you push them as available through the availability endpoint.
Only if a day is send as available AND a price is defined in the rate plans, it is shown as bookable on holidu.
If you need to understand how often to send the availability data, please refer to the page Update schedule