You cannot guess the unique ID. You must obtain it by navigating properly through Google Maps.
A properly formatted Google contributions profile URL typically contains parameters that authenticate the user and specify the view. The fragment authuser=0 indicates the default account signed into the browser (where 0 represents the first account). The terms contributions and profile suggest a page listing every public action a user has taken: business reviews, uploaded photos, answered questions, added missing places, or corrected map data. In essence, this is a —a record of how an individual has helped refine the world’s most used digital map.