get/show Last ID

to have the ID, you can try this hook e.g.

add_action("save_post", function ($post_ID, $post, $update) {


    if (    !$update
        &&  class_exists("Flamingo_Inbound_Message")
        &&  (Flamingo_Inbound_Message::post_type === $post->post_type)
    ) {

        // here $post_ID is the ID of the new created inbound message


    }


}, 10, 3);