How can my customer select the quantity for a resource? For example, I have a room with 3 beds and would like him to book for 1, 2 or 3 people.

The resources do not have a quantity selector, but in this specific case, you can combine it with the people options.

You’ll have to set up the bed as a resource and set “3” in the availability value (see this page for the resource settings) and add the resource to your bookable product as explained here.

Then, you can set up the people options on the product to accept a minimum of 1 and a maximum of 3 people (please, read this page for more details about the people settings).

Additionally, you must make sure that the option “Count people as separate bookings” is enabled (read more about this option here).

Now, the user will be able to select the number of people for that bed and therefore the bed availability will be correctly updated when a booking is done.