error CS1061: Type `System.Collections.Generic.List<System.Collections.Generic.List<int>>' does'nt contain a def for `GetLength' and no extension mthd

Question

im coding in C# and getting

does not contain a definition for GetLength' and no extension method GetLength' of type

in HACKERRANK...the same code is executable([and giving correct answer][1]) on Visual Studio 2019 and not working on HackerRank Compiler.I have this problem several time while working with arrays on HackerRank & I used Count ...But in 2D Array the Count didn't work.

public static int diagonalDifference(List<List<int>> arr)
{
        int sumRight=0;
        int sumLeft=0;
        //sum of left Diagonal
        for(int i=0;i<arr.GetLength(0);i++)
        {
            for(int j=i;j<arr.GetLength(1);j++)
            {
                sumRight = sumRight + arr[i, j];
                break;
            }
        }
        //Console.WriteLine(sumRight);
        
        //Sum of Left diagonal
        int p = -1;
        for (int i=arr.GetLength(1)-1;i>=0;i--)
        { 
            p = p + 1;
            for(int j=p;j<arr.GetLength(0);j++)
            {
                sumLeft = sumLeft + arr[j, i];
                break;
            }             
        }
        //Console.WriteLine(sumLeft);
        
        //calculate diagonal difference
        int absolute = sumRight - sumLeft;
        int abpos = Math.Abs(absolute);
        return abpos;

}