Full Code

BackndRank.cs

using System.Collections.Generic;
using System.Text;
using UnityEngine;

// Adds BACKND SDK namespace
using BACKND;

public class BackndRank {
    private static BackndRank _instance = null;

    public static BackndRank Instance {
        get {
            if(_instance == null) {
                _instance = new BackndRank();
            }

            return _instance;
        }
    }

    public void LeaderboardInsert(int score) {
        // [Change required] Change the 'copied UUID value' to the UUID value of the ranking created in 'BACKND Console > Ranking Management.'
        string rankUUID = "Copied UUID value"; // Example: "4088f640-693e-11ed-ad29-ad8f0c3d4c70"

        string tableName = "USER_DATA";
        string rowInDate = string.Empty;

        // The inDate value of the data used in the game data is required to insert a ranking.  
        // Therefore, you must load the data and extract its inDate value.  
        Debug.Log("Attempts data lookup.");
        var bro = Backnd.PlayerTable.GetMyData(tableName);

        if(bro.IsSuccess() == false) {
            Debug.LogError("An error has occurred while looking up data : " + bro);
            return;
        }

        Debug.Log("Data lookup successful : " + bro);

        if(bro.FlattenRows().Count > 0) {
            rowInDate = bro.FlattenRows()[0]["inDate"].ToString();
        } else {
            Debug.Log("The data does not exist. Attempting data insertion.");
            var bro2 = Backnd.PlayerTable.Insert(tableName);

            if(bro2.IsSuccess() == false) {
                Debug.LogError("An error occurred while inserting data : " + bro2);
                return;
            }

            Debug.Log("Data insertion successful : " + bro2);

            rowInDate = bro2.GetInDate();
        }

        Debug.Log("rowInDate of my game information : " + rowInDate); // The extracted rowIndate value is as follows:

        Param param = new Param();
        param.Add("level", score);

        // Edits the data with the extracted rowIndate to the param value and updates the data for the ranking.  
        Debug.Log("Attempting ranking insertion.");
        var rankBro = Backnd.Leaderboard.Player.UpdateMyDataAndRefreshLeaderboard(rankUUID, tableName, rowInDate, param);

        if(rankBro.IsSuccess() == false) {
            Debug.LogError("An error has occurred while registering the ranking. : " + rankBro);
            return;
        }

        Debug.Log("Successfully inserted the ranking. : " + rankBro);
    }

    public void RankGet() {
        string rankUUID = "Copied UUID value"; // Example: "4088f640-693e-11ed-ad29-ad8f0c3d4c70"
        var bro = Backnd.Leaderboard.Player.GetRankList(rankUUID);

        if(bro.IsSuccess() == false) {
            Debug.LogError("An error occurred while looking up rankings. : " + bro);
            return;
        }

        Debug.Log("Ranking lookup successful. : " + bro);

        Debug.Log("Total number of users registered to the ranking : " + bro.GetFlattenJSON()["totalCount"].ToString());

        foreach(BACKND.LitJson.JsonData jsonData in bro.FlattenRows()) {
            StringBuilder info = new StringBuilder();

            info.AppendLine("Ranking : " + jsonData["rank"].ToString());
            info.AppendLine("Nickname : " + jsonData["nickname"].ToString());
            info.AppendLine("Score : " + jsonData["score"].ToString());
            info.AppendLine("gamerInDate : " + jsonData["gamerInDate"].ToString());
            info.AppendLine("Sort code : " + jsonData["index"].ToString());
            info.AppendLine();
            Debug.Log(info);
        }
    }
}

BackndManager.cs

using UnityEngine;
using System.Threading.Tasks;

// Adds BACKND SDK namespace
using BACKND;

public class BackndManager : MonoBehaviour {
    void Start() {
        var bro = Backnd.Initialize(); // Initialize BACKND

        // Response value for BACKND initialization
        if(bro.IsSuccess()) {
            Debug.Log("Initialization successful : " + bro); // If successful, 'statusCode 204 Success'
        } else {
            Debug.LogError("Initialization failed : " + bro); // If failed, a 4xx statusCode error occurs 
        }

        Test();
    }

    // A method that allows synchronous methods to be called from asynchronous methods(cannot be accessed by the Unity UI)
    async void Test() {
        await Task.Run(() => {
            BackndLogin.Instance.CustomSignIn("user1", "1234"); // BACKND login method

            BackndRank.Instance.LeaderboardInsert(100); // [Addition] Ranking registration method
            BackndRank.Instance.RankGet(); // [Addition] Ranking loading method
            
            Debug.Log("Test complete.");
        });
    }
}

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