This function is available as part of the elloha Magic subscription.
It is not unusual for a search on your booking engine for your establishment not to return any availability for a given day: this does not mean that you have no rooms available, but that your rooms cannot accommodate the number of "pax" (occupants) requested, for example, or that they cannot accommodate them for the number of days requested.
An example? I'm looking for 2 people for 3 nights from Monday, but my establishment has no rooms available - from Monday - for 3 consecutive nights. In this case, the booking engine returns the following response: "Sorry, we have no availability for these dates".
From now on, with flex on dates, your booking engine will be able to suggest other available dates before or after the requested date if the other search values (number of people, length of stay, age of travellers, etc.) are validated.