using jquery autocomplete in wordpress plugin

Auto complete is most likely not working on the extra fields because they are added with javascript dynamically, and when you make your javascript .autocomplete() call, it runs on page load. Your dynamically created fields do not exist yet to have autocomplete hooked with them. Try this.

jQuery(document).on("keydown", ".post_email_repeatable", function(){
    jQuery(this).autocomplete({
        source: "get_posts.php",
        minLength: 1
    });
});

This binds the autocomplete function the input field with that class whenever the keydown event happens on it. So it will trigger even when keydown event happens on newly dynamically created fields.

Also as Milo commented, you should use a class as ID’s should be unique, however not having unique IDs shouldnt break the functionality of it. I still suggest you add a “post_email_repeatable” class to each repeatable field.