Take the list id from the url on the Make a List page for your list.

curl -X GET "<https://unduel.com/api/v1/list/latest-rankings?listId=><list id>&user=<user name>" \\
  -H "X-API-Key: <api key>"

interface LatestRankingsResponse {
  /** List metadata */
  createdAt: string;   
  updatedAt: string;   
  name: string;        
  nameRef: string; // slug
  title?: string | null;
  tierListTitle?: string | null;
  description?: string | null;      
  prompt?: string | null;           
  shouldUseImages: boolean;
  shouldShowNames: boolean;
  shouldShowItemSubtitles: boolean;
  allowAnonymousVoting: boolean;
  isHidden: boolean;
  topicId: string;                  

  /** The item set this list ranks */
  itemSet: {
    id: string;                     
    name: string;                  
    nameSingular?: string | null;   
    nameRef: string; // slug
    imageUrl?: string | null;       
  };

  parentListId?: string | null;     

  /** Tags applied to the list */
  tags: {
    isNegative: boolean; // true ⇢ exclusion tag
    tag: {
      id: string;   
      name: string;          
      nameRef: string; // slug
      color?: string | null;   
      isItem: boolean;  
    };
  }[];

  /** Most-recent snapshot (null until the first snapshot exists) */
  latestSnapshot?: {
    id: string;   
    createdAt: string;     
    itemCount: number;      
    voteCount: number;     
    voterCount: number;     

    /** Items in ascending rank order */
    listRankingItemSnapshots: {
      itemId: string;   
      rank: number; // 1 = best
      rating: string; // decimal 0-1, **returned as string**
      standardDeviation: string; // decimal, **returned as string**
      voterCount: number;
      tierValue?: number | null; // 1 (F) … 6 (S)
      blendProportion: string; // decimal 0-1, **string**

      /** Item metadata (lite) */
      item: {
        id: string;
        name: string;
        nameRef: string; // slug
        subtitle?: string | null;
        imageUrl?: string | null;
        imageWidth?: number | null;
        imageHeight?: number | null;
        pixelated?: boolean | null;
        description?: string | null;
        properties?: string | null; // arbitrary JSON
        source?: string | null; // wiki url
        isArchived: boolean;

        /** Tags on the item */
        tags: {
          tag: {
            id: string;
            name: string;
            nameRef: // slug
            color?: string | null;
            isItem: boolean;
          };
        }[];
      };
    }[];
  } | null;
}