Listing attributes can be marked so that the user can search for them in his database and on his website. Therefore, in this code, the listing number is copied to the listing attribute after the listing is created.
Since then it is possible to search for a listing using their number and display that number in the listing content or with a shortcode. In my opinion, this can be helpful with a large number of listings to make sure in communication with the client which listing we are talking about.
As in the description, you first need to create a listing attribute "“numer_ogloszenia” (which means listing_number) (or other attribute name and change it in the code).
You can display this attribute in the listing content like other attributes, e.g. %label%: #%value%