I develop a travel agency website and I am using ACF pro. I started to add my fields and my itineraries can have some multi destinations as “Singapore, Thailand”, I would like to know if I can use my field as a slug to build my URL :
There isn’t anything in ACF that will allow you to use values of fields as part of your URL string (slugs).
It is possible to do, but it’s complicated and beyond the scope of this forum. I can give you a basic idea of what’s involved.
First you need to create custom rewrite rules and custom url. Once you get that working then you need to build a pre_get_posts filter and a template redirect action that will cause WP to query for the correct post and show the right template. There is a basic outline of this here https://premium.wpmudev.org/blog/building-customized-urls-wordpress/